如何使用 ms access 数据库在 c# windows 表单中添加条件语句？
How to add a conditional statement in a c# windows form with a ms access database?
我正在使用连接到 Microsoft Access 数据库的 c# windows 表单应用程序。如果 txtSupplyLeft 小于 5，我希望 txtOrderMore 文本框显示“是”，如果 txtSupplyLeft 大于 5，则显示“否”。我希望在将新记录插入数据库后发生这种情况。这是我想出的
private void btnSave_Click(object sender, EventArgs e)
{
try
{
connection.Open();
OleDbCommand command = new OleDbCommand();
command.Connection = connection;
command.CommandText = "insert into Products (ProductName, ProductPrice, Quantity, [Weight(g)], DaysSupplyLeft) values ('"+txtProductName.Text+"', "+txtProductPrice.Text+ ", " + txtQuantity.Text + ", " + txtWeight.Text + ", " + txtSupplyLeft.Text + ")";
command.ExecuteNonQuery();
txtProductName.Text = "";
txtProductPrice.Text = "";
txtQuantity.Text = "";
txtWeight.Text = "";
txtSupplyLeft.Text = "";
MessageBox.Show("Data saved");
connection.Close();
}
catch (Exception ex)
{
MessageBox.Show("Error" + ex);
}
try
{
connection.Open();
OleDbCommand command = new OleDbCommand();
command.Connection = connection;
command.CommandText = "insert into Products ([OrderMore?]) values ('Yes') where "+txtSupplyLeft.Text+"<5";
command.ExecuteNonQuery();
txtOrderMore.Text = "Yes";
MessageBox.Show("Data saved");
connection.Close();
}
catch (Exception ex)
{
MessageBox.Show("Error" + ex);
}
try
{
connection.Open();
OleDbCommand command = new OleDbCommand();
command.Connection = connection;
command.CommandText = "insert into Products ([OrderMore?]) values ('No') where "+txtSupplyLeft.Text+"";
command.ExecuteNonQuery();
txtOrderMore.Text = "No";
connection.Close();
}
catch(Exception ex)
{
MessageBox.Show("Error" + ex);
}
}
但是每当我 运行 这段代码时，输出“是”的条件不起作用，a.k.a 当我输入一个小于 5 的值时，我从来没有得到一个是。它确实输出不，但每当我保存一条新记录时，我都会收到连接异常，当我在每个尝试循环的末尾明确添加“connection.Close()”时，它告诉我连接尚未关闭。
我对 windows 表单和 SQL 查询非常陌生，因此我不太确定哪里出了问题。
在推荐参数化查询之前，我已经看到很多评论，但我不太确定该怎么做。
在 OleDbCommand 中使用参数时，了解以下内容很重要：
The OLE DB .NET Provider does not support named parameters for passing
parameters to an SQL statement or a stored procedure called by an
OleDbCommand when CommandType is set to Text. In this case, the
question mark (?) placeholder must be used. For example:
SELECT * FROM Customers WHERE CustomerID = ?
Therefore, the order in which OleDbParameter objects are added to the
OleDbParameterCollection must directly correspond to the position of
the question mark placeholder for the parameter in the command text.
下面，我将展示如何向 Access 数据库中插入数据，以及如何更新 Access 数据库中的数据。我将在整个代码中使用 OleDbParameter。
访问数据库名称:Database1.accdb
在 Access（设计视图）中，
Table 姓名: 产品
- ID: 自动编号
- ProductName：短文本（常规选项卡 => 字段大小：50）
- 价格：货币（常规选项卡 => 格式：货币）
- 数量：数量
- 体重(g): 数量
- 剩余供应天数：数量
- ReorderWhenQuantityReaches: 数量
- OrderMore：Yes/No（常规选项卡 => 格式：Yes/No）
如果以编程方式创建 table ，请使用以下列定义：
Table 姓名: 产品
- ID: AutoIncrement not null Primary Key
- 产品名称：varchar(50) 不为空
- 价格：货币
- 数量：整数
- 体重(g):整数
- 剩余供应天数：整数
- ReorderWhenQuantityReaches：整数
- 订单更多:位
注意：在以编程方式创建 table 之后，要使其在 Access 中看起来像需要的那样，可能需要更改“格式”属性 对于某些字段（列）。在 Access 中打开数据库。右键单击“产品”。 Select“设计视图”。然后按照上面“在 Access（设计视图）”中所述设置属性。
在您的 VS 项目中，确保您的项目具有 System.Data.
的引用
VS 2019:
- 在 VS 菜单中，单击 项目
- Select 添加引用
- 单击程序集
- 勾选System.Data
创建一个名为 HelperAccess
的 class
- 在 VS 菜单中，单击 项目
- Select 添加Class...（名称：HelperAccess.cs）
将以下 using 语句添加到 HelperAccess.cs:
using System.Data.OleDb;
在“HelperAccess.cs”中添加以下变量：
private string _databaseFilename = string.Empty;
private string _connectionString = string.Empty;
然后添加如下构造函数：
public HelperAccess(string databaseFilename)
{
_databaseFilename = databaseFilename;
_connectionString = String.Format("Provider = Microsoft.ACE.OLEDB.12.0; Data Source = {0};Persist Security Info=False;", _databaseFilename);
}
在“HelperAccess.cs”中，创建一个名为AddProduct的方法，添加一个变量到return，并添加return语句
public int AddProduct(string productName, decimal price, int quantity, double weightInGrams, int daysSupplyLeft, int reorderWhenQuantityReaches, bool orderMore = false)
{
int result = 0;
return result;
}
我们将从创建 SQL 开始，这样我们就知道需要指定哪些参数了。
string sqlText = "INSERT INTO Product (ProductName, Price, Quantity, [Weight(g)], DaysSupplyLeft, ReorderWhenQuantityReaches, OrderMore) VALUES(?, ?, ?, ?, ?, ?, ?)";
接下来，我们将创建 OleDbConnection 的实例并打开连接。当使用 using 语句时，它确保对象在执行超出范围时关闭 and/or 处置。
public int AddProduct(string productName, decimal price, int quantity, double weightInGrams, int daysSupplyLeft, int reorderWhenQuantityReaches, bool orderMore = false)
{
int result = 0;
string sqlText = "INSERT INTO Product (ProductName, Price, Quantity, [Weight(g)], DaysSupplyLeft, ReorderWhenQuantityReaches, OrderMore) VALUES(?, ?, ?, ?, ?, ?, ?)";
using (OleDbConnection con = new OleDbConnection(_connectionString))
{
//open connection
con.Open();
}
return result;
}
现在，我们将在 OleDbConnection 的实例中创建一个 OleDbCommand 的实例。
public int AddProduct(string productName, decimal price, int quantity, double weightInGrams, int daysSupplyLeft, int reorderWhenQuantityReaches, bool orderMore = false)
{
int result = 0;
string sqlText = "INSERT INTO Product (ProductName, Price, Quantity, [Weight(g)], DaysSupplyLeft, ReorderWhenQuantityReaches, OrderMore) VALUES(?, ?, ?, ?, ?, ?, ?)";
using (OleDbConnection con = new OleDbConnection(_connectionString))
{
//open connection
con.Open();
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
}
}
return result;
}
让我们看看如何声明一个参数。首先，创建 OleDbParameter.
的新实例
OleDbParameter paramProductName = new OleDbParameter();
现在，设置属性。为数据库列设置正确的数据类型很重要。虽然 OleDbCommand 不使用“ParameterName”，但我选择设置 属性 因为它使调试更容易。如果未设置该值，该值将显示为“Parameter1”、“Parameter2”等...
根据Set the field size（访问），
- 长整型 — 适用于范围从 -2,147,483,648 到 +2,147,483,647 的整数。存储要求是四个字节。
Data types for Access desktop databases
- Currency：货币数据，以4位小数精度存储。 8个
字节
- Yes/No：布尔型（true/false）数据； Access 存储数字
值为零 (0) 表示假，-1 表示真。 1 个字节。
并根据Integral numeric types (C# reference)
- int -2,147,483,648 到 2,147,483,647 有符号 32 位整数 System.Int32
我们还需要看看OleDbType Enum
BigInt：64 位有符号整数 (DBTYPE_I8)。这映射到 Int64。
布尔值：一个布尔值
货币: 一个货币值...
十进制:
Double: 一个浮点数...
整数：32 位有符号整数 (DBTYPE_I4)。这映射到 Int32。
OleDbParameter paramProductName = new OleDbParameter();
paramProductName.OleDbType = OleDbType.VarChar;
paramProductName.ParameterName = "@productName";
paramProductName.Value = 产品名称；
要将 属性 添加到我们的 OleDbCommand (sqlCmd) 实例，我们执行以下操作：
sqlCmd.Parameters.Add(paramProductName);
这是我们目前所拥有的：
public int AddProduct(string productName, decimal price, int quantity, double weightInGrams, int daysSupplyLeft, int reorderWhenQuantityReaches, bool orderMore = false)
{
int result = 0;
string sqlText = "INSERT INTO Product (ProductName, Price, Quantity, [Weight(g)], DaysSupplyLeft, ReorderWhenQuantityReaches, OrderMore) VALUES(?, ?, ?, ?, ?, ?, ?)";
using (OleDbConnection con = new OleDbConnection(_connectionString))
{
//open connection
con.Open();
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
OleDbParameter paramProductName = new OleDbParameter();
paramProductName.OleDbType = OleDbType.VarChar;
paramProductName.ParameterName = "@productName";
paramProductName.Value = productName;
//add parameter
sqlCmd.Parameters.Add(paramProductName);
}
}
return result;
}
现在，我们可以添加其余参数，请记住，必须按照使用（引用）的顺序添加它们。在我们开始之前，让我们看看如何执行 SQL.
执行SQL:
result = sqlCmd.ExecuteNonQuery();
添加产品:
public int AddProduct(string productName, decimal price, int quantity, double weightInGrams, int daysSupplyLeft, int reorderWhenQuantityReaches, bool orderMore = false)
{
int result = 0;
string sqlText = "INSERT INTO Product (ProductName, Price, Quantity, [Weight(g)], DaysSupplyLeft, ReorderWhenQuantityReaches, OrderMore) VALUES(?, ?, ?, ?, ?, ?, ?)";
using (OleDbConnection con = new OleDbConnection(_connectionString))
{
//open connection
con.Open();
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//ProductName
OleDbParameter paramProductName = new OleDbParameter();
paramProductName.OleDbType = OleDbType.VarChar;
paramProductName.ParameterName = "@productName";
paramProductName.Value = productName;
//add parameter
sqlCmd.Parameters.Add(paramProductName);
//Price
OleDbParameter paramPrice = new OleDbParameter();
paramPrice.OleDbType = OleDbType.Currency;
paramPrice.ParameterName = "@price";
paramPrice.Value = price;
//add parameter
sqlCmd.Parameters.Add(paramPrice);
//Quantity
OleDbParameter paramQuantity = new OleDbParameter();
paramQuantity.OleDbType = OleDbType.Integer;
paramQuantity.ParameterName = "@quantity";
paramQuantity.Value = quantity;
//add parameter
sqlCmd.Parameters.Add(paramQuantity);
//Weight(g)
OleDbParameter paramWeight = new OleDbParameter();
paramWeight.OleDbType = OleDbType.Double;
paramWeight.ParameterName = "@weight";
paramWeight.Value = weightInGrams;
//add parameter
sqlCmd.Parameters.Add(paramWeight);
//DaysSupplyLeft
OleDbParameter paramDaysSupplyLeft = new OleDbParameter();
paramDaysSupplyLeft.OleDbType = OleDbType.Integer;
paramDaysSupplyLeft.ParameterName = "@daysSupplyLeft";
paramDaysSupplyLeft.Value = daysSupplyLeft;
//add parameter
sqlCmd.Parameters.Add(paramDaysSupplyLeft);
//ReorderWhenSupplyReaches
OleDbParameter paramReorderWhenQuantityReaches = new OleDbParameter();
paramReorderWhenQuantityReaches.OleDbType = OleDbType.Integer;
paramReorderWhenQuantityReaches.ParameterName = "@reorderWhenQuantityReaches";
paramReorderWhenQuantityReaches.Value = reorderWhenQuantityReaches;
//add parameter
sqlCmd.Parameters.Add(paramReorderWhenQuantityReaches);
//orderMore
OleDbParameter paramOrderMore = new OleDbParameter();
paramOrderMore.OleDbType = OleDbType.Boolean;
paramOrderMore.ParameterName = "@orderMore";
paramOrderMore.Value = orderMore;
//add parameter
sqlCmd.Parameters.Add(paramOrderMore);
//execute command
result = sqlCmd.ExecuteNonQuery();
}
}
return result;
}
现在让我们看看如何对数据库执行更新table。在“HelperAccess.cs”
中创建名为 UpdateProductQuantity 的方法
public int UpdateProductQuantity(int id, int quantity)
{
}
创建 SQL:
string sqlText = "UPDATE Product SET Quantity = ? WHERE ID = ?";
其余代码与前面的方法类似，不再赘述。
更新产品数量:
public int UpdateProductQuantity(int id, int quantity)
{
string sqlText = "UPDATE Product SET Quantity = ? WHERE ID = ?";
int result = 0;
using (OleDbConnection con = new OleDbConnection(_connectionString))
{
//open connection
con.Open();
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//Note: Parameters MUST be added in the order that they are used (referenced) since
//ParameterName isn't used by OleDbCommand. However, setting the
//ParameterName property can be useful for debugging
// Quantity
OleDbParameter paramQuantity = new OleDbParameter();
paramQuantity.OleDbType = OleDbType.Integer;
paramQuantity.ParameterName = "@quantity";
//calculate quantity remaining and set value
paramQuantity.Value = quantity;
//add parameter
sqlCmd.Parameters.Add(paramQuantity);
//ID
OleDbParameter paramId = new OleDbParameter();
paramId.OleDbType = OleDbType.Integer;
paramId.ParameterName = "@id";
paramId.Value = id;
//add parameter
sqlCmd.Parameters.Add(paramId);
//execute command
result = sqlCmd.ExecuteNonQuery();
}
}
return result;
}
我们如何使用代码更新数量？如果客户进行购买，我们将要更新数量。可以获取当前数量，减去购买数量，并更新数据库。然后，如果数量低于 Product table 中“ReorderWhenQuantityReaches”中指定的数量，我们会将“OrderMore”的值设置为“Yes”并引发订阅者可以侦听的事件。这可用于更新表单上的 OrderMore 文本框。
让我们创建一个方法来从产品中获取现有数量 table。由于这是更新过程的一部分，我们可以打开一次连接，然后在我们获取数量的方法中使用该连接。
在“HelperAccess.cs”中，创建一个名为GetCurrentQuantity的方法，向return添加一个变量，并添加return语句。
public int GetCurrentQuantity(OleDbConnection con, int id)
{
int currentQuantity = 0;
return currentQuantity;
}
创建 SQL 查询：
string sqlText = "SELECT quantity from Product where ID = ?";
创建OleDbCommand实例，并添加id参数：
public int GetCurrentQuantity(OleDbConnection con, int id)
{
int currentQuantity = 0;
string sqlText = "SELECT quantity from Product where ID = ?";
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//ID
OleDbParameter paramId = new OleDbParameter();
paramId.OleDbType = OleDbType.Integer;
paramId.ParameterName = "@id";
paramId.Value = id;
//add parameter
sqlCmd.Parameters.Add(paramId);
}
return currentQuantity;
}
有多种方法可以从数据库中读取值。我们将使用 OleDbDataReader。创建 OleDbReader 的新实例并使用它来获取值。该列可以通过其列名或在查询中的相对位置来引用。该指数是从零开始的。由于我们只指定一列，索引为零。
GetCurrentQuantity:
public int GetCurrentQuantity(OleDbConnection con, int id)
{
int currentQuantity = 0;
string sqlText = "SELECT quantity from Product where ID = ?";
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//ID
OleDbParameter paramId = new OleDbParameter();
paramId.OleDbType = OleDbType.Integer;
paramId.ParameterName = "@id";
paramId.Value = id;
//add parameter
sqlCmd.Parameters.Add(paramId);
//get value
using (OleDbDataReader reader = sqlCmd.ExecuteReader())
{
while (reader.Read())
{
currentQuantity = (int)reader[0];
}
}
}
return currentQuantity;
}
接下来，让我们创建一个方法，在数量变化时更新“OrderMore”的值。我们将获得数量的当前值。我们还需要知道是什么数量“触发”了要更改的“OrderMore”的值。该值存储在“ReorderWhenQuantityReaches”中，因此我们需要检索该值并将其与数量进行比较。完成比较后，我们可以引发事件 (OrderMoreValueUpdated) 以通知订阅者“OrderMore”的值是“是”还是“否”。
在我们继续之前，因为我们将在我们的方法中引发一个事件，所以让我们看看如何创建一个可以订阅的事件。我不会详细介绍事件，因为人们可以找到很多关于它们的 articles/posts。我将只显示需要添加以使其工作的代码。在“HelperAccess.cs”的顶部添加以下代码：
public class HelperAccess
{
public delegate void EventHandlerOrderMoreValueUpdated(object sender, string e);
//event that subscribers can subscribe to
public event EventHandlerOrderMoreValueUpdated OrderMoreValueUpdated;
...
}
引发事件的方法如下：
//check if event has subscribers
if (OrderMoreValueUpdated != null)
{
//raise event
OrderMoreValueUpdated(this, "test");
}
现在我们准备创建我们的方法 UpdateOrderMore。由于我已经涵盖了代码的不同部分，所以我将只展示完成的方法。
更新订单更多
public int UpdateOrderMore(OleDbConnection con, int id)
{
string sqlText = string.Empty;
int reorderWhenQuantityReaches = 0;
int result = 0;
//get Quantity
int currentQuantity = GetCurrentQuantity(con, id);
//get ReorderWhenQuantityReaches
sqlText = "SELECT ReorderWhenQuantityReaches from Product where ID = ?";
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//ParameterName isn't used by OleDbCommand. However, setting the
//ParameterName property can be useful for debugging
//ID
OleDbParameter paramId = new OleDbParameter();
paramId.OleDbType = OleDbType.Integer;
paramId.ParameterName = "@id";
paramId.Value = id;
//add parameter
sqlCmd.Parameters.Add(paramId);
//get value
using (OleDbDataReader reader = sqlCmd.ExecuteReader())
{
while (reader.Read())
{
reorderWhenQuantityReaches = (int)reader[0];
}
}
}
sqlText = "UPDATE Product SET OrderMore = ? WHERE ID = ?";
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//Note: Parameters MUST be added in the order that they are used (referenced) since
//ParameterName isn't used by OleDbCommand. However, setting the
//ParameterName property can be useful for debugging
//if quantity is below value specified in ReorderWhenQuantityReaches, then
//set OrderMore to true (Yes)
bool orderMoreVal = false;
string orderMoreValStr = string.Empty;
if (currentQuantity <= reorderWhenQuantityReaches)
{
orderMoreVal = true;
orderMoreValStr = "Yes";
}
else
{
orderMoreVal = false;
orderMoreValStr = "No";
}
//OrderMore
OleDbParameter paramOrderMore = new OleDbParameter();
paramOrderMore.OleDbType = OleDbType.Boolean;
paramOrderMore.ParameterName = "@orderMore";
paramOrderMore.Value = orderMoreVal;
//add parameter
sqlCmd.Parameters.Add(paramOrderMore);
//ID
OleDbParameter paramId = new OleDbParameter();
paramId.OleDbType = OleDbType.Integer;
paramId.ParameterName = "@id";
paramId.Value = id;
//add parameter
sqlCmd.Parameters.Add(paramId);
//execute command
result = sqlCmd.ExecuteNonQuery();
//check if event has subscribers
if (OrderMoreValueUpdated != null)
{
//raise event
OrderMoreValueUpdated(this, orderMoreValStr);
}
}
return result;
}
最后，这里有一个合并上述代码的方法。作为完成销售的一部分，当前数量需要减去购买的数量。然后我们将检查是否需要订购更多产品并报告结果。
购买后更新产品数量
public int UpdateProductQuantityAfterPurchase(int id, int quantityPurchased)
{
string sqlText = "UPDATE Product SET Quantity = ? WHERE ID = ?";
int resultUpdateQuantity = 0;
using (OleDbConnection con = new OleDbConnection(_connectionString))
{
//open connection
con.Open();
//get current quantity
int currentQuantity = GetCurrentQuantity(con, id);
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//Note: Parameters MUST be added in the order that they are used (referenced) since
//ParameterName isn't used by OleDbCommand. However, setting the
//ParameterName property can be useful for debugging
// Quantity
OleDbParameter paramQuantity = new OleDbParameter();
paramQuantity.OleDbType = OleDbType.Integer;
paramQuantity.ParameterName = "@quantity";
//calculate quantity remaining and set value
paramQuantity.Value = currentQuantity - quantityPurchased;
//add parameter
sqlCmd.Parameters.Add(paramQuantity);
//ID
OleDbParameter paramId = new OleDbParameter();
paramId.OleDbType = OleDbType.Integer;
paramId.ParameterName = "@id";
paramId.Value = id;
//add parameter
sqlCmd.Parameters.Add(paramId);
//execute command
resultUpdateQuantity = sqlCmd.ExecuteNonQuery();
if (resultUpdateQuantity > 0)
{
System.Diagnostics.Debug.WriteLine("Info: " + resultUpdateQuantity + " row updated.");
}
}
//update OrderMore
int resultUpdateOrderMore = UpdateOrderMore(con, id);
}
return resultUpdateQuantity;
}
由于 post 的字符限制，我无法在“Helper.cs”中添加方法的所有代码，但代码在上面。 “Helper.cs”的布局应类似于以下内容（“...”是代码所在的位置）：
HelperAccess.cs
public class HelperAccess
{
private string _databaseFilename = string.Empty;
private string _connectionString = string.Empty;
public delegate void EventHandlerOrderMoreValueUpdated(object sender, string e);
//event that subscribers can subscribe to
public event EventHandlerOrderMoreValueUpdated OrderMoreValueUpdated;
public HelperAccess(string databaseFilename)
{
_databaseFilename = databaseFilename;
_connectionString = String.Format("Provider = Microsoft.ACE.OLEDB.12.0; Data Source = {0};Persist Security Info=False;", _databaseFilename);
}
public int AddProduct(string productName, decimal price, int quantity, double weightInGrams, int daysSupplyLeft, int reorderWhenQuantityReaches, bool orderMore = false)
{
...
}
public int GetCurrentQuantity(OleDbConnection con, int id)
{
...
}
public int UpdateProductQuantity(int id, int quantity)
{
...
}
public int UpdateProductQuantityAfterPurchase(int id, int quantityPurchased)
{
...
}
public int UpdateOrderMore(OleDbConnection con, int id)
{
...
}
}
用法
为了测试，我在 Form1 中添加了以下内容：
以下 TextBox 控件已添加到 Form1：
- 名称：textBoxId
- 名称：textBoxProductName
- 名称：文本框价格
- 名称：文本框数量
- 名称：textBoxWeight
- 名称：textBoxReorderWhenQuantityReaches
- 名称：textBoxDaysSupplyLeft
- 名称：textBoxOrderMore（只读：true）
注意: 我还在每个TextBox的左边添加了一个Label。
最后，我添加了一个按钮（名称：btnSave）到Form1.cs
Form1.cs:
public partial class Form1 : Form
{
private static string _databaseFilename = @"C:\Users\Test\Documents\Database1.accdb";
private HelperAccess _helperAccess = null;
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
//create new instance
_helperAccess = new HelperAccess(_databaseFilename);
//subscribe to event
_helperAccess.OrderMoreValueUpdated += _helperAccess_OrderMoreValueUpdated;
}
private void _helperAccess_OrderMoreValueUpdated(object sender, string e)
{
//needed for cross-threaded operations
if (textBoxOrderMore.InvokeRequired)
{
textBoxOrderMore.Invoke((MethodInvoker) delegate
{
textBoxOrderMore.Text = (string)e;
textBoxOrderMore.Refresh();
});
}
else
{
textBoxOrderMore.Text = (string)e;
textBoxOrderMore.Refresh();
}
}
private void AddProduct()
{
//convert price
decimal price = 0;
Decimal.TryParse(textBoxPrice.Text, out price);
//convert quantity
int quantity = 0;
Int32.TryParse(textBoxQuantity.Text, out quantity);
//convert weight
double weight = 0;
Double.TryParse(textBoxWeight.Text, out weight);
//convert days supply left
int daysSupplyLeft = 0;
Int32.TryParse(textBoxDaysSupplyLeft.Text, out daysSupplyLeft);
//convert reorder when quantity reaches
int reorderWhenQuantityReaches = 0;
Int32.TryParse(textBoxReorderWhenQuantityReaches.Text, out reorderWhenQuantityReaches);
//add product to database
int result = _helperAccess.AddProduct(textBoxProductName.Text, price, quantity, weight, daysSupplyLeft, reorderWhenQuantityReaches);
}
private void btnSave_Click(object sender, EventArgs e)
{
AddProduct();
}
}
要使用 UpdateProductQuantityAfterPurchase：
_helperAccess.UpdateProductQuantityAfterPurchase(id, 1);
我正在使用连接到 Microsoft Access 数据库的 c# windows 表单应用程序。如果 txtSupplyLeft 小于 5，我希望 txtOrderMore 文本框显示“是”，如果 txtSupplyLeft 大于 5，则显示“否”。我希望在将新记录插入数据库后发生这种情况。这是我想出的
private void btnSave_Click(object sender, EventArgs e)
{
try
{
connection.Open();
OleDbCommand command = new OleDbCommand();
command.Connection = connection;
command.CommandText = "insert into Products (ProductName, ProductPrice, Quantity, [Weight(g)], DaysSupplyLeft) values ('"+txtProductName.Text+"', "+txtProductPrice.Text+ ", " + txtQuantity.Text + ", " + txtWeight.Text + ", " + txtSupplyLeft.Text + ")";
command.ExecuteNonQuery();
txtProductName.Text = "";
txtProductPrice.Text = "";
txtQuantity.Text = "";
txtWeight.Text = "";
txtSupplyLeft.Text = "";
MessageBox.Show("Data saved");
connection.Close();
}
catch (Exception ex)
{
MessageBox.Show("Error" + ex);
}
try
{
connection.Open();
OleDbCommand command = new OleDbCommand();
command.Connection = connection;
command.CommandText = "insert into Products ([OrderMore?]) values ('Yes') where "+txtSupplyLeft.Text+"<5";
command.ExecuteNonQuery();
txtOrderMore.Text = "Yes";
MessageBox.Show("Data saved");
connection.Close();
}
catch (Exception ex)
{
MessageBox.Show("Error" + ex);
}
try
{
connection.Open();
OleDbCommand command = new OleDbCommand();
command.Connection = connection;
command.CommandText = "insert into Products ([OrderMore?]) values ('No') where "+txtSupplyLeft.Text+"";
command.ExecuteNonQuery();
txtOrderMore.Text = "No";
connection.Close();
}
catch(Exception ex)
{
MessageBox.Show("Error" + ex);
}
}
但是每当我 运行 这段代码时，输出“是”的条件不起作用，a.k.a 当我输入一个小于 5 的值时，我从来没有得到一个是。它确实输出不，但每当我保存一条新记录时，我都会收到连接异常，当我在每个尝试循环的末尾明确添加“connection.Close()”时，它告诉我连接尚未关闭。 我对 windows 表单和 SQL 查询非常陌生，因此我不太确定哪里出了问题。 在推荐参数化查询之前，我已经看到很多评论，但我不太确定该怎么做。
在 OleDbCommand 中使用参数时，了解以下内容很重要：
The OLE DB .NET Provider does not support named parameters for passing parameters to an SQL statement or a stored procedure called by an OleDbCommand when CommandType is set to Text. In this case, the question mark (?) placeholder must be used. For example:
SELECT * FROM Customers WHERE CustomerID = ?
Therefore, the order in which OleDbParameter objects are added to the OleDbParameterCollection must directly correspond to the position of the question mark placeholder for the parameter in the command text.
下面，我将展示如何向 Access 数据库中插入数据，以及如何更新 Access 数据库中的数据。我将在整个代码中使用 OleDbParameter。
访问数据库名称:Database1.accdb
在 Access（设计视图）中，
Table 姓名: 产品
- ID: 自动编号
- ProductName：短文本（常规选项卡 => 字段大小：50）
- 价格：货币（常规选项卡 => 格式：货币）
- 数量：数量
- 体重(g): 数量
- 剩余供应天数：数量
- ReorderWhenQuantityReaches: 数量
- OrderMore：Yes/No（常规选项卡 => 格式：Yes/No）
如果以编程方式创建 table ，请使用以下列定义：
Table 姓名: 产品
- ID: AutoIncrement not null Primary Key
- 产品名称：varchar(50) 不为空
- 价格：货币
- 数量：整数
- 体重(g):整数
- 剩余供应天数：整数
- ReorderWhenQuantityReaches：整数
- 订单更多:位
注意：在以编程方式创建 table 之后，要使其在 Access 中看起来像需要的那样，可能需要更改“格式”属性 对于某些字段（列）。在 Access 中打开数据库。右键单击“产品”。 Select“设计视图”。然后按照上面“在 Access（设计视图）”中所述设置属性。
在您的 VS 项目中，确保您的项目具有 System.Data.
VS 2019:
- 在 VS 菜单中，单击 项目
- Select 添加引用
- 单击程序集
- 勾选System.Data
创建一个名为 HelperAccess
的 class- 在 VS 菜单中，单击 项目
- Select 添加Class...（名称：HelperAccess.cs）
将以下 using 语句添加到 HelperAccess.cs:
using System.Data.OleDb;
在“HelperAccess.cs”中添加以下变量：
private string _databaseFilename = string.Empty;
private string _connectionString = string.Empty;
然后添加如下构造函数：
public HelperAccess(string databaseFilename)
{
_databaseFilename = databaseFilename;
_connectionString = String.Format("Provider = Microsoft.ACE.OLEDB.12.0; Data Source = {0};Persist Security Info=False;", _databaseFilename);
}
在“HelperAccess.cs”中，创建一个名为AddProduct的方法，添加一个变量到return，并添加return语句
public int AddProduct(string productName, decimal price, int quantity, double weightInGrams, int daysSupplyLeft, int reorderWhenQuantityReaches, bool orderMore = false)
{
int result = 0;
return result;
}
我们将从创建 SQL 开始，这样我们就知道需要指定哪些参数了。
string sqlText = "INSERT INTO Product (ProductName, Price, Quantity, [Weight(g)], DaysSupplyLeft, ReorderWhenQuantityReaches, OrderMore) VALUES(?, ?, ?, ?, ?, ?, ?)";
接下来，我们将创建 OleDbConnection 的实例并打开连接。当使用 using 语句时，它确保对象在执行超出范围时关闭 and/or 处置。
public int AddProduct(string productName, decimal price, int quantity, double weightInGrams, int daysSupplyLeft, int reorderWhenQuantityReaches, bool orderMore = false)
{
int result = 0;
string sqlText = "INSERT INTO Product (ProductName, Price, Quantity, [Weight(g)], DaysSupplyLeft, ReorderWhenQuantityReaches, OrderMore) VALUES(?, ?, ?, ?, ?, ?, ?)";
using (OleDbConnection con = new OleDbConnection(_connectionString))
{
//open connection
con.Open();
}
return result;
}
现在，我们将在 OleDbConnection 的实例中创建一个 OleDbCommand 的实例。
public int AddProduct(string productName, decimal price, int quantity, double weightInGrams, int daysSupplyLeft, int reorderWhenQuantityReaches, bool orderMore = false)
{
int result = 0;
string sqlText = "INSERT INTO Product (ProductName, Price, Quantity, [Weight(g)], DaysSupplyLeft, ReorderWhenQuantityReaches, OrderMore) VALUES(?, ?, ?, ?, ?, ?, ?)";
using (OleDbConnection con = new OleDbConnection(_connectionString))
{
//open connection
con.Open();
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
}
}
return result;
}
让我们看看如何声明一个参数。首先，创建 OleDbParameter.
OleDbParameter paramProductName = new OleDbParameter();
现在，设置属性。为数据库列设置正确的数据类型很重要。虽然 OleDbCommand 不使用“ParameterName”，但我选择设置 属性 因为它使调试更容易。如果未设置该值，该值将显示为“Parameter1”、“Parameter2”等...
根据Set the field size（访问），
- 长整型 — 适用于范围从 -2,147,483,648 到 +2,147,483,647 的整数。存储要求是四个字节。
Data types for Access desktop databases
- Currency：货币数据，以4位小数精度存储。 8个 字节
- Yes/No：布尔型（true/false）数据； Access 存储数字 值为零 (0) 表示假，-1 表示真。 1 个字节。
并根据Integral numeric types (C# reference)
- int -2,147,483,648 到 2,147,483,647 有符号 32 位整数 System.Int32
我们还需要看看OleDbType Enum
BigInt：64 位有符号整数 (DBTYPE_I8)。这映射到 Int64。
布尔值：一个布尔值
货币: 一个货币值...
十进制:
Double: 一个浮点数...
整数：32 位有符号整数 (DBTYPE_I4)。这映射到 Int32。
OleDbParameter paramProductName = new OleDbParameter(); paramProductName.OleDbType = OleDbType.VarChar; paramProductName.ParameterName = "@productName"; paramProductName.Value = 产品名称；
要将 属性 添加到我们的 OleDbCommand (sqlCmd) 实例，我们执行以下操作：
sqlCmd.Parameters.Add(paramProductName);
这是我们目前所拥有的：
public int AddProduct(string productName, decimal price, int quantity, double weightInGrams, int daysSupplyLeft, int reorderWhenQuantityReaches, bool orderMore = false)
{
int result = 0;
string sqlText = "INSERT INTO Product (ProductName, Price, Quantity, [Weight(g)], DaysSupplyLeft, ReorderWhenQuantityReaches, OrderMore) VALUES(?, ?, ?, ?, ?, ?, ?)";
using (OleDbConnection con = new OleDbConnection(_connectionString))
{
//open connection
con.Open();
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
OleDbParameter paramProductName = new OleDbParameter();
paramProductName.OleDbType = OleDbType.VarChar;
paramProductName.ParameterName = "@productName";
paramProductName.Value = productName;
//add parameter
sqlCmd.Parameters.Add(paramProductName);
}
}
return result;
}
现在，我们可以添加其余参数，请记住，必须按照使用（引用）的顺序添加它们。在我们开始之前，让我们看看如何执行 SQL.
执行SQL:
result = sqlCmd.ExecuteNonQuery();
添加产品:
public int AddProduct(string productName, decimal price, int quantity, double weightInGrams, int daysSupplyLeft, int reorderWhenQuantityReaches, bool orderMore = false)
{
int result = 0;
string sqlText = "INSERT INTO Product (ProductName, Price, Quantity, [Weight(g)], DaysSupplyLeft, ReorderWhenQuantityReaches, OrderMore) VALUES(?, ?, ?, ?, ?, ?, ?)";
using (OleDbConnection con = new OleDbConnection(_connectionString))
{
//open connection
con.Open();
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//ProductName
OleDbParameter paramProductName = new OleDbParameter();
paramProductName.OleDbType = OleDbType.VarChar;
paramProductName.ParameterName = "@productName";
paramProductName.Value = productName;
//add parameter
sqlCmd.Parameters.Add(paramProductName);
//Price
OleDbParameter paramPrice = new OleDbParameter();
paramPrice.OleDbType = OleDbType.Currency;
paramPrice.ParameterName = "@price";
paramPrice.Value = price;
//add parameter
sqlCmd.Parameters.Add(paramPrice);
//Quantity
OleDbParameter paramQuantity = new OleDbParameter();
paramQuantity.OleDbType = OleDbType.Integer;
paramQuantity.ParameterName = "@quantity";
paramQuantity.Value = quantity;
//add parameter
sqlCmd.Parameters.Add(paramQuantity);
//Weight(g)
OleDbParameter paramWeight = new OleDbParameter();
paramWeight.OleDbType = OleDbType.Double;
paramWeight.ParameterName = "@weight";
paramWeight.Value = weightInGrams;
//add parameter
sqlCmd.Parameters.Add(paramWeight);
//DaysSupplyLeft
OleDbParameter paramDaysSupplyLeft = new OleDbParameter();
paramDaysSupplyLeft.OleDbType = OleDbType.Integer;
paramDaysSupplyLeft.ParameterName = "@daysSupplyLeft";
paramDaysSupplyLeft.Value = daysSupplyLeft;
//add parameter
sqlCmd.Parameters.Add(paramDaysSupplyLeft);
//ReorderWhenSupplyReaches
OleDbParameter paramReorderWhenQuantityReaches = new OleDbParameter();
paramReorderWhenQuantityReaches.OleDbType = OleDbType.Integer;
paramReorderWhenQuantityReaches.ParameterName = "@reorderWhenQuantityReaches";
paramReorderWhenQuantityReaches.Value = reorderWhenQuantityReaches;
//add parameter
sqlCmd.Parameters.Add(paramReorderWhenQuantityReaches);
//orderMore
OleDbParameter paramOrderMore = new OleDbParameter();
paramOrderMore.OleDbType = OleDbType.Boolean;
paramOrderMore.ParameterName = "@orderMore";
paramOrderMore.Value = orderMore;
//add parameter
sqlCmd.Parameters.Add(paramOrderMore);
//execute command
result = sqlCmd.ExecuteNonQuery();
}
}
return result;
}
现在让我们看看如何对数据库执行更新table。在“HelperAccess.cs”
中创建名为 UpdateProductQuantity 的方法public int UpdateProductQuantity(int id, int quantity)
{
}
创建 SQL:
string sqlText = "UPDATE Product SET Quantity = ? WHERE ID = ?";
其余代码与前面的方法类似，不再赘述。
更新产品数量:
public int UpdateProductQuantity(int id, int quantity)
{
string sqlText = "UPDATE Product SET Quantity = ? WHERE ID = ?";
int result = 0;
using (OleDbConnection con = new OleDbConnection(_connectionString))
{
//open connection
con.Open();
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//Note: Parameters MUST be added in the order that they are used (referenced) since
//ParameterName isn't used by OleDbCommand. However, setting the
//ParameterName property can be useful for debugging
// Quantity
OleDbParameter paramQuantity = new OleDbParameter();
paramQuantity.OleDbType = OleDbType.Integer;
paramQuantity.ParameterName = "@quantity";
//calculate quantity remaining and set value
paramQuantity.Value = quantity;
//add parameter
sqlCmd.Parameters.Add(paramQuantity);
//ID
OleDbParameter paramId = new OleDbParameter();
paramId.OleDbType = OleDbType.Integer;
paramId.ParameterName = "@id";
paramId.Value = id;
//add parameter
sqlCmd.Parameters.Add(paramId);
//execute command
result = sqlCmd.ExecuteNonQuery();
}
}
return result;
}
我们如何使用代码更新数量？如果客户进行购买，我们将要更新数量。可以获取当前数量，减去购买数量，并更新数据库。然后，如果数量低于 Product table 中“ReorderWhenQuantityReaches”中指定的数量，我们会将“OrderMore”的值设置为“Yes”并引发订阅者可以侦听的事件。这可用于更新表单上的 OrderMore 文本框。
让我们创建一个方法来从产品中获取现有数量 table。由于这是更新过程的一部分，我们可以打开一次连接，然后在我们获取数量的方法中使用该连接。
在“HelperAccess.cs”中，创建一个名为GetCurrentQuantity的方法，向return添加一个变量，并添加return语句。
public int GetCurrentQuantity(OleDbConnection con, int id)
{
int currentQuantity = 0;
return currentQuantity;
}
创建 SQL 查询：
string sqlText = "SELECT quantity from Product where ID = ?";
创建OleDbCommand实例，并添加id参数：
public int GetCurrentQuantity(OleDbConnection con, int id)
{
int currentQuantity = 0;
string sqlText = "SELECT quantity from Product where ID = ?";
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//ID
OleDbParameter paramId = new OleDbParameter();
paramId.OleDbType = OleDbType.Integer;
paramId.ParameterName = "@id";
paramId.Value = id;
//add parameter
sqlCmd.Parameters.Add(paramId);
}
return currentQuantity;
}
有多种方法可以从数据库中读取值。我们将使用 OleDbDataReader。创建 OleDbReader 的新实例并使用它来获取值。该列可以通过其列名或在查询中的相对位置来引用。该指数是从零开始的。由于我们只指定一列，索引为零。
GetCurrentQuantity:
public int GetCurrentQuantity(OleDbConnection con, int id)
{
int currentQuantity = 0;
string sqlText = "SELECT quantity from Product where ID = ?";
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//ID
OleDbParameter paramId = new OleDbParameter();
paramId.OleDbType = OleDbType.Integer;
paramId.ParameterName = "@id";
paramId.Value = id;
//add parameter
sqlCmd.Parameters.Add(paramId);
//get value
using (OleDbDataReader reader = sqlCmd.ExecuteReader())
{
while (reader.Read())
{
currentQuantity = (int)reader[0];
}
}
}
return currentQuantity;
}
接下来，让我们创建一个方法，在数量变化时更新“OrderMore”的值。我们将获得数量的当前值。我们还需要知道是什么数量“触发”了要更改的“OrderMore”的值。该值存储在“ReorderWhenQuantityReaches”中，因此我们需要检索该值并将其与数量进行比较。完成比较后，我们可以引发事件 (OrderMoreValueUpdated) 以通知订阅者“OrderMore”的值是“是”还是“否”。
在我们继续之前，因为我们将在我们的方法中引发一个事件，所以让我们看看如何创建一个可以订阅的事件。我不会详细介绍事件，因为人们可以找到很多关于它们的 articles/posts。我将只显示需要添加以使其工作的代码。在“HelperAccess.cs”的顶部添加以下代码：
public class HelperAccess
{
public delegate void EventHandlerOrderMoreValueUpdated(object sender, string e);
//event that subscribers can subscribe to
public event EventHandlerOrderMoreValueUpdated OrderMoreValueUpdated;
...
}
引发事件的方法如下：
//check if event has subscribers
if (OrderMoreValueUpdated != null)
{
//raise event
OrderMoreValueUpdated(this, "test");
}
现在我们准备创建我们的方法 UpdateOrderMore。由于我已经涵盖了代码的不同部分，所以我将只展示完成的方法。
更新订单更多
public int UpdateOrderMore(OleDbConnection con, int id)
{
string sqlText = string.Empty;
int reorderWhenQuantityReaches = 0;
int result = 0;
//get Quantity
int currentQuantity = GetCurrentQuantity(con, id);
//get ReorderWhenQuantityReaches
sqlText = "SELECT ReorderWhenQuantityReaches from Product where ID = ?";
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//ParameterName isn't used by OleDbCommand. However, setting the
//ParameterName property can be useful for debugging
//ID
OleDbParameter paramId = new OleDbParameter();
paramId.OleDbType = OleDbType.Integer;
paramId.ParameterName = "@id";
paramId.Value = id;
//add parameter
sqlCmd.Parameters.Add(paramId);
//get value
using (OleDbDataReader reader = sqlCmd.ExecuteReader())
{
while (reader.Read())
{
reorderWhenQuantityReaches = (int)reader[0];
}
}
}
sqlText = "UPDATE Product SET OrderMore = ? WHERE ID = ?";
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//Note: Parameters MUST be added in the order that they are used (referenced) since
//ParameterName isn't used by OleDbCommand. However, setting the
//ParameterName property can be useful for debugging
//if quantity is below value specified in ReorderWhenQuantityReaches, then
//set OrderMore to true (Yes)
bool orderMoreVal = false;
string orderMoreValStr = string.Empty;
if (currentQuantity <= reorderWhenQuantityReaches)
{
orderMoreVal = true;
orderMoreValStr = "Yes";
}
else
{
orderMoreVal = false;
orderMoreValStr = "No";
}
//OrderMore
OleDbParameter paramOrderMore = new OleDbParameter();
paramOrderMore.OleDbType = OleDbType.Boolean;
paramOrderMore.ParameterName = "@orderMore";
paramOrderMore.Value = orderMoreVal;
//add parameter
sqlCmd.Parameters.Add(paramOrderMore);
//ID
OleDbParameter paramId = new OleDbParameter();
paramId.OleDbType = OleDbType.Integer;
paramId.ParameterName = "@id";
paramId.Value = id;
//add parameter
sqlCmd.Parameters.Add(paramId);
//execute command
result = sqlCmd.ExecuteNonQuery();
//check if event has subscribers
if (OrderMoreValueUpdated != null)
{
//raise event
OrderMoreValueUpdated(this, orderMoreValStr);
}
}
return result;
}
最后，这里有一个合并上述代码的方法。作为完成销售的一部分，当前数量需要减去购买的数量。然后我们将检查是否需要订购更多产品并报告结果。
购买后更新产品数量
public int UpdateProductQuantityAfterPurchase(int id, int quantityPurchased)
{
string sqlText = "UPDATE Product SET Quantity = ? WHERE ID = ?";
int resultUpdateQuantity = 0;
using (OleDbConnection con = new OleDbConnection(_connectionString))
{
//open connection
con.Open();
//get current quantity
int currentQuantity = GetCurrentQuantity(con, id);
using (OleDbCommand sqlCmd = new OleDbCommand(sqlText, con))
{
//Note: Parameters MUST be added in the order that they are used (referenced) since
//ParameterName isn't used by OleDbCommand. However, setting the
//ParameterName property can be useful for debugging
// Quantity
OleDbParameter paramQuantity = new OleDbParameter();
paramQuantity.OleDbType = OleDbType.Integer;
paramQuantity.ParameterName = "@quantity";
//calculate quantity remaining and set value
paramQuantity.Value = currentQuantity - quantityPurchased;
//add parameter
sqlCmd.Parameters.Add(paramQuantity);
//ID
OleDbParameter paramId = new OleDbParameter();
paramId.OleDbType = OleDbType.Integer;
paramId.ParameterName = "@id";
paramId.Value = id;
//add parameter
sqlCmd.Parameters.Add(paramId);
//execute command
resultUpdateQuantity = sqlCmd.ExecuteNonQuery();
if (resultUpdateQuantity > 0)
{
System.Diagnostics.Debug.WriteLine("Info: " + resultUpdateQuantity + " row updated.");
}
}
//update OrderMore
int resultUpdateOrderMore = UpdateOrderMore(con, id);
}
return resultUpdateQuantity;
}
由于 post 的字符限制，我无法在“Helper.cs”中添加方法的所有代码，但代码在上面。 “Helper.cs”的布局应类似于以下内容（“...”是代码所在的位置）：
HelperAccess.cs
public class HelperAccess
{
private string _databaseFilename = string.Empty;
private string _connectionString = string.Empty;
public delegate void EventHandlerOrderMoreValueUpdated(object sender, string e);
//event that subscribers can subscribe to
public event EventHandlerOrderMoreValueUpdated OrderMoreValueUpdated;
public HelperAccess(string databaseFilename)
{
_databaseFilename = databaseFilename;
_connectionString = String.Format("Provider = Microsoft.ACE.OLEDB.12.0; Data Source = {0};Persist Security Info=False;", _databaseFilename);
}
public int AddProduct(string productName, decimal price, int quantity, double weightInGrams, int daysSupplyLeft, int reorderWhenQuantityReaches, bool orderMore = false)
{
...
}
public int GetCurrentQuantity(OleDbConnection con, int id)
{
...
}
public int UpdateProductQuantity(int id, int quantity)
{
...
}
public int UpdateProductQuantityAfterPurchase(int id, int quantityPurchased)
{
...
}
public int UpdateOrderMore(OleDbConnection con, int id)
{
...
}
}
用法
为了测试，我在 Form1 中添加了以下内容：
以下 TextBox 控件已添加到 Form1：
- 名称：textBoxId
- 名称：textBoxProductName
- 名称：文本框价格
- 名称：文本框数量
- 名称：textBoxWeight
- 名称：textBoxReorderWhenQuantityReaches
- 名称：textBoxDaysSupplyLeft
- 名称：textBoxOrderMore（只读：true）
注意: 我还在每个TextBox的左边添加了一个Label。
最后，我添加了一个按钮（名称：btnSave）到Form1.cs
Form1.cs:
public partial class Form1 : Form
{
private static string _databaseFilename = @"C:\Users\Test\Documents\Database1.accdb";
private HelperAccess _helperAccess = null;
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
//create new instance
_helperAccess = new HelperAccess(_databaseFilename);
//subscribe to event
_helperAccess.OrderMoreValueUpdated += _helperAccess_OrderMoreValueUpdated;
}
private void _helperAccess_OrderMoreValueUpdated(object sender, string e)
{
//needed for cross-threaded operations
if (textBoxOrderMore.InvokeRequired)
{
textBoxOrderMore.Invoke((MethodInvoker) delegate
{
textBoxOrderMore.Text = (string)e;
textBoxOrderMore.Refresh();
});
}
else
{
textBoxOrderMore.Text = (string)e;
textBoxOrderMore.Refresh();
}
}
private void AddProduct()
{
//convert price
decimal price = 0;
Decimal.TryParse(textBoxPrice.Text, out price);
//convert quantity
int quantity = 0;
Int32.TryParse(textBoxQuantity.Text, out quantity);
//convert weight
double weight = 0;
Double.TryParse(textBoxWeight.Text, out weight);
//convert days supply left
int daysSupplyLeft = 0;
Int32.TryParse(textBoxDaysSupplyLeft.Text, out daysSupplyLeft);
//convert reorder when quantity reaches
int reorderWhenQuantityReaches = 0;
Int32.TryParse(textBoxReorderWhenQuantityReaches.Text, out reorderWhenQuantityReaches);
//add product to database
int result = _helperAccess.AddProduct(textBoxProductName.Text, price, quantity, weight, daysSupplyLeft, reorderWhenQuantityReaches);
}
private void btnSave_Click(object sender, EventArgs e)
{
AddProduct();
}
}
要使用 UpdateProductQuantityAfterPurchase：
_helperAccess.UpdateProductQuantityAfterPurchase(id, 1);