在 SQLite (Flutter) 中更新字段
Updating field in SQLite (Flutter)
让我们以此code snippet为例。数据模型非常简单：
class Dog {
final int id;
final String name;
final int age;
Dog({this.id, this.name, this.age});
}
为了更新信息，我正在使用这个功能：
Future<void> updateDog(Dog dog) async {
// Get a reference to the database.
final db = await database;
// Update the given Dog.
await db.update(
'dogs',
dog.toMap(),
// Ensure that the Dog has a matching id.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [dog.id],
);
}
await updateDog(Dog(id: 0, name: 'Fido', age: 42));
它工作得很好，没有任何问题。现在的问题是，如何在不使用name的情况下更新only字段age？所以基本上我想做这样的事情
await updateDog(Dog(id: 0, age: 35));
并期待结果 "name: Figo, age: 35"。但相反，它删除了 null 中的 Fido。所以我得到了这个结果："name: null, age: 35".
您可以复制粘贴 运行 下面的完整代码
示例代码有两条记录来演示更新效果
解决方案 1：您可以使用 rawUpdate
代码片段
int count = await db.rawUpdate('UPDATE dogs SET age = ? WHERE id = ?', [35, 0]);
解决方案 2：您可以将 toMap 修改为仅 return id 和 age
Future<void> updateDog1(Dog dog) async {
// Get a reference to the database.
final db = await database;
// Update the given Dog.
await db.update(
'dogs',
dog.toMap1(),
...
Map<String, dynamic> toMap1() {
return {
'id': id,
'age': age,
};
}
fido = Dog(
id: fido.id,
name: "not care",
age: 35,
);
await updateDog1(fido);
输出
I/flutter ( 6570): [Dog{id: 0, name: Fido, age: 42}, Dog{id: 1, name: abc, age: 10}]
I/flutter ( 6570): updated: 1
I/flutter ( 6570): [Dog{id: 0, name: Fido, age: 35}, Dog{id: 1, name: abc, age: 10}]
完整代码解决方案1
import 'dart:async';
import 'package:flutter/widgets.dart';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
void main() async {
// Avoid errors caused by flutter upgrade.
// Importing 'package:flutter/widgets.dart' is required.
WidgetsFlutterBinding.ensureInitialized();
final database = openDatabase(
// Set the path to the database. Note: Using the `join` function from the
// `path` package is best practice to ensure the path is correctly
// constructed for each platform.
join(await getDatabasesPath(), 'doggie_database.db'),
// When the database is first created, create a table to store dogs.
onCreate: (db, version) {
return db.execute(
"CREATE TABLE dogs(id INTEGER PRIMARY KEY, name TEXT, age INTEGER)",
);
},
// Set the version. This executes the onCreate function and provides a
// path to perform database upgrades and downgrades.
version: 1,
);
Future<void> insertDog(Dog dog) async {
// Get a reference to the database.
final Database db = await database;
// Insert the Dog into the correct table. Also specify the
// `conflictAlgorithm`. In this case, if the same dog is inserted
// multiple times, it replaces the previous data.
await db.insert(
'dogs',
dog.toMap(),
conflictAlgorithm: ConflictAlgorithm.replace,
);
}
Future<List<Dog>> dogs() async {
// Get a reference to the database.
final Database db = await database;
// Query the table for all The Dogs.
final List<Map<String, dynamic>> maps = await db.query('dogs');
// Convert the List<Map<String, dynamic> into a List<Dog>.
return List.generate(maps.length, (i) {
return Dog(
id: maps[i]['id'],
name: maps[i]['name'],
age: maps[i]['age'],
);
});
}
Future<void> updateDog(Dog dog) async {
// Get a reference to the database.
final db = await database;
// Update the given Dog.
await db.update(
'dogs',
dog.toMap(),
// Ensure that the Dog has a matching id.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [dog.id],
);
}
Future<void> deleteDog(int id) async {
// Get a reference to the database.
final db = await database;
// Remove the Dog from the database.
await db.delete(
'dogs',
// Use a `where` clause to delete a specific dog.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [id],
);
}
var fido = Dog(
id: 0,
name: 'Fido',
age: 42,
);
var fido1 = Dog(
id: 1,
name: 'abc',
age: 10,
);
// Insert a dog into the database.
await insertDog(fido);
await insertDog(fido1);
// Print the list of dogs (only Fido for now).
print(await dogs());
/*
// Update Fido's age and save it to the database.
fido = Dog(
id: fido.id,
name: fido.name,
age: fido.age + 7,
);
await updateDog(fido);
// Print Fido's updated information.
print(await dogs());*/
final Database db = await database;
int count =
await db.rawUpdate('UPDATE dogs SET age = ? WHERE id = ?', [35, 0]);
print('updated: $count');
print(await dogs());
/*// Delete Fido from the database.
await deleteDog(fido.id);
// Print the list of dogs (empty).
print(await dogs());*/
}
class Dog {
final int id;
final String name;
final int age;
Dog({this.id, this.name, this.age});
Map<String, dynamic> toMap() {
return {
'id': id,
'name': name,
'age': age,
};
}
// Implement toString to make it easier to see information about
// each dog when using the print statement.
@override
String toString() {
return 'Dog{id: $id, name: $name, age: $age}';
}
}
完整代码解决方案2
import 'dart:async';
import 'package:flutter/widgets.dart';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
void main() async {
// Avoid errors caused by flutter upgrade.
// Importing 'package:flutter/widgets.dart' is required.
WidgetsFlutterBinding.ensureInitialized();
final database = openDatabase(
// Set the path to the database. Note: Using the `join` function from the
// `path` package is best practice to ensure the path is correctly
// constructed for each platform.
join(await getDatabasesPath(), 'doggie_database.db'),
// When the database is first created, create a table to store dogs.
onCreate: (db, version) {
return db.execute(
"CREATE TABLE dogs(id INTEGER PRIMARY KEY, name TEXT, age INTEGER)",
);
},
// Set the version. This executes the onCreate function and provides a
// path to perform database upgrades and downgrades.
version: 1,
);
Future<void> insertDog(Dog dog) async {
// Get a reference to the database.
final Database db = await database;
// Insert the Dog into the correct table. Also specify the
// `conflictAlgorithm`. In this case, if the same dog is inserted
// multiple times, it replaces the previous data.
await db.insert(
'dogs',
dog.toMap(),
conflictAlgorithm: ConflictAlgorithm.replace,
);
}
Future<List<Dog>> dogs() async {
// Get a reference to the database.
final Database db = await database;
// Query the table for all The Dogs.
final List<Map<String, dynamic>> maps = await db.query('dogs');
// Convert the List<Map<String, dynamic> into a List<Dog>.
return List.generate(maps.length, (i) {
return Dog(
id: maps[i]['id'],
name: maps[i]['name'],
age: maps[i]['age'],
);
});
}
Future<void> updateDog(Dog dog) async {
// Get a reference to the database.
final db = await database;
// Update the given Dog.
await db.update(
'dogs',
dog.toMap(),
// Ensure that the Dog has a matching id.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [dog.id],
);
}
Future<void> updateDog1(Dog dog) async {
// Get a reference to the database.
final db = await database;
// Update the given Dog.
await db.update(
'dogs',
dog.toMap1(),
// Ensure that the Dog has a matching id.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [dog.id],
);
}
Future<void> deleteDog(int id) async {
// Get a reference to the database.
final db = await database;
// Remove the Dog from the database.
await db.delete(
'dogs',
// Use a `where` clause to delete a specific dog.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [id],
);
}
var fido = Dog(
id: 0,
name: 'Fido',
age: 42,
);
var fido1 = Dog(
id: 1,
name: 'abc',
age: 10,
);
// Insert a dog into the database.
await insertDog(fido);
await insertDog(fido1);
// Print the list of dogs (only Fido for now).
print(await dogs());
// Update Fido's age and save it to the database.
fido = Dog(
id: fido.id,
name: "not care",
age: 35,
);
await updateDog1(fido);
// Print Fido's updated information.
print(await dogs());
/*final Database db = await database;
int count =
await db.rawUpdate('UPDATE dogs SET age = ? WHERE id = ?', [35, 0]);
print('updated: $count');
print(await dogs());*/
/*// Delete Fido from the database.
await deleteDog(fido.id);
// Print the list of dogs (empty).
print(await dogs());*/
}
class Dog {
final int id;
final String name;
final int age;
Dog({this.id, this.name, this.age});
Map<String, dynamic> toMap() {
return {
'id': id,
'name': name,
'age': age,
};
}
Map<String, dynamic> toMap1() {
return {
'id': id,
'age': age,
};
}
// Implement toString to make it easier to see information about
// each dog when using the print statement.
@override
String toString() {
return 'Dog{id: $id, name: $name, age: $age}';
}
}
文档中的示例如下所示：
// Update Fido's age and save it to the database.
fido = Dog(
id: fido.id,
name: fido.name,
age: fido.age + 7,
);
await updateDog(fido);
您要么像 chunhunghan 的回答那样使用原始 SQL 查询来处理它，要么
使用 id 查询狗，然后覆盖字段，然后更新。
为什么？
让我们看看您的更新代码：
await updateDog(Dog(id: 0, age: 35));
调用更新行时，将调用 Dog.toMap()，看起来您正在将名称更新为 null。
你可以在这里做你想做的是代码：
Future<Dog> getDog(int id) async {
List<Map> result = await database.query(..... whereArgs: [id]);
if (result.length > 0) {
return new Dog.fromMap(result.first);
}
return null;
}
// Now in code
fido = await getDog(id);
// Update Fido's age and save it to the database.
fido = Dog(
id: fido.id,
name: fido.name,
age: 35, //<--
);
await updateDog(fido);
让我们以此code snippet为例。数据模型非常简单：
class Dog {
final int id;
final String name;
final int age;
Dog({this.id, this.name, this.age});
}
为了更新信息，我正在使用这个功能：
Future<void> updateDog(Dog dog) async {
// Get a reference to the database.
final db = await database;
// Update the given Dog.
await db.update(
'dogs',
dog.toMap(),
// Ensure that the Dog has a matching id.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [dog.id],
);
}
await updateDog(Dog(id: 0, name: 'Fido', age: 42));
它工作得很好，没有任何问题。现在的问题是，如何在不使用name的情况下更新only字段age？所以基本上我想做这样的事情
await updateDog(Dog(id: 0, age: 35));
并期待结果 "name: Figo, age: 35"。但相反，它删除了 null 中的 Fido。所以我得到了这个结果："name: null, age: 35".
您可以复制粘贴 运行 下面的完整代码
示例代码有两条记录来演示更新效果
解决方案 1：您可以使用 rawUpdate
代码片段
int count = await db.rawUpdate('UPDATE dogs SET age = ? WHERE id = ?', [35, 0]);
解决方案 2：您可以将 toMap 修改为仅 return id 和 age
Future<void> updateDog1(Dog dog) async {
// Get a reference to the database.
final db = await database;
// Update the given Dog.
await db.update(
'dogs',
dog.toMap1(),
...
Map<String, dynamic> toMap1() {
return {
'id': id,
'age': age,
};
}
fido = Dog(
id: fido.id,
name: "not care",
age: 35,
);
await updateDog1(fido);
输出
I/flutter ( 6570): [Dog{id: 0, name: Fido, age: 42}, Dog{id: 1, name: abc, age: 10}]
I/flutter ( 6570): updated: 1
I/flutter ( 6570): [Dog{id: 0, name: Fido, age: 35}, Dog{id: 1, name: abc, age: 10}]
完整代码解决方案1
import 'dart:async';
import 'package:flutter/widgets.dart';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
void main() async {
// Avoid errors caused by flutter upgrade.
// Importing 'package:flutter/widgets.dart' is required.
WidgetsFlutterBinding.ensureInitialized();
final database = openDatabase(
// Set the path to the database. Note: Using the `join` function from the
// `path` package is best practice to ensure the path is correctly
// constructed for each platform.
join(await getDatabasesPath(), 'doggie_database.db'),
// When the database is first created, create a table to store dogs.
onCreate: (db, version) {
return db.execute(
"CREATE TABLE dogs(id INTEGER PRIMARY KEY, name TEXT, age INTEGER)",
);
},
// Set the version. This executes the onCreate function and provides a
// path to perform database upgrades and downgrades.
version: 1,
);
Future<void> insertDog(Dog dog) async {
// Get a reference to the database.
final Database db = await database;
// Insert the Dog into the correct table. Also specify the
// `conflictAlgorithm`. In this case, if the same dog is inserted
// multiple times, it replaces the previous data.
await db.insert(
'dogs',
dog.toMap(),
conflictAlgorithm: ConflictAlgorithm.replace,
);
}
Future<List<Dog>> dogs() async {
// Get a reference to the database.
final Database db = await database;
// Query the table for all The Dogs.
final List<Map<String, dynamic>> maps = await db.query('dogs');
// Convert the List<Map<String, dynamic> into a List<Dog>.
return List.generate(maps.length, (i) {
return Dog(
id: maps[i]['id'],
name: maps[i]['name'],
age: maps[i]['age'],
);
});
}
Future<void> updateDog(Dog dog) async {
// Get a reference to the database.
final db = await database;
// Update the given Dog.
await db.update(
'dogs',
dog.toMap(),
// Ensure that the Dog has a matching id.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [dog.id],
);
}
Future<void> deleteDog(int id) async {
// Get a reference to the database.
final db = await database;
// Remove the Dog from the database.
await db.delete(
'dogs',
// Use a `where` clause to delete a specific dog.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [id],
);
}
var fido = Dog(
id: 0,
name: 'Fido',
age: 42,
);
var fido1 = Dog(
id: 1,
name: 'abc',
age: 10,
);
// Insert a dog into the database.
await insertDog(fido);
await insertDog(fido1);
// Print the list of dogs (only Fido for now).
print(await dogs());
/*
// Update Fido's age and save it to the database.
fido = Dog(
id: fido.id,
name: fido.name,
age: fido.age + 7,
);
await updateDog(fido);
// Print Fido's updated information.
print(await dogs());*/
final Database db = await database;
int count =
await db.rawUpdate('UPDATE dogs SET age = ? WHERE id = ?', [35, 0]);
print('updated: $count');
print(await dogs());
/*// Delete Fido from the database.
await deleteDog(fido.id);
// Print the list of dogs (empty).
print(await dogs());*/
}
class Dog {
final int id;
final String name;
final int age;
Dog({this.id, this.name, this.age});
Map<String, dynamic> toMap() {
return {
'id': id,
'name': name,
'age': age,
};
}
// Implement toString to make it easier to see information about
// each dog when using the print statement.
@override
String toString() {
return 'Dog{id: $id, name: $name, age: $age}';
}
}
完整代码解决方案2
import 'dart:async';
import 'package:flutter/widgets.dart';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
void main() async {
// Avoid errors caused by flutter upgrade.
// Importing 'package:flutter/widgets.dart' is required.
WidgetsFlutterBinding.ensureInitialized();
final database = openDatabase(
// Set the path to the database. Note: Using the `join` function from the
// `path` package is best practice to ensure the path is correctly
// constructed for each platform.
join(await getDatabasesPath(), 'doggie_database.db'),
// When the database is first created, create a table to store dogs.
onCreate: (db, version) {
return db.execute(
"CREATE TABLE dogs(id INTEGER PRIMARY KEY, name TEXT, age INTEGER)",
);
},
// Set the version. This executes the onCreate function and provides a
// path to perform database upgrades and downgrades.
version: 1,
);
Future<void> insertDog(Dog dog) async {
// Get a reference to the database.
final Database db = await database;
// Insert the Dog into the correct table. Also specify the
// `conflictAlgorithm`. In this case, if the same dog is inserted
// multiple times, it replaces the previous data.
await db.insert(
'dogs',
dog.toMap(),
conflictAlgorithm: ConflictAlgorithm.replace,
);
}
Future<List<Dog>> dogs() async {
// Get a reference to the database.
final Database db = await database;
// Query the table for all The Dogs.
final List<Map<String, dynamic>> maps = await db.query('dogs');
// Convert the List<Map<String, dynamic> into a List<Dog>.
return List.generate(maps.length, (i) {
return Dog(
id: maps[i]['id'],
name: maps[i]['name'],
age: maps[i]['age'],
);
});
}
Future<void> updateDog(Dog dog) async {
// Get a reference to the database.
final db = await database;
// Update the given Dog.
await db.update(
'dogs',
dog.toMap(),
// Ensure that the Dog has a matching id.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [dog.id],
);
}
Future<void> updateDog1(Dog dog) async {
// Get a reference to the database.
final db = await database;
// Update the given Dog.
await db.update(
'dogs',
dog.toMap1(),
// Ensure that the Dog has a matching id.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [dog.id],
);
}
Future<void> deleteDog(int id) async {
// Get a reference to the database.
final db = await database;
// Remove the Dog from the database.
await db.delete(
'dogs',
// Use a `where` clause to delete a specific dog.
where: "id = ?",
// Pass the Dog's id as a whereArg to prevent SQL injection.
whereArgs: [id],
);
}
var fido = Dog(
id: 0,
name: 'Fido',
age: 42,
);
var fido1 = Dog(
id: 1,
name: 'abc',
age: 10,
);
// Insert a dog into the database.
await insertDog(fido);
await insertDog(fido1);
// Print the list of dogs (only Fido for now).
print(await dogs());
// Update Fido's age and save it to the database.
fido = Dog(
id: fido.id,
name: "not care",
age: 35,
);
await updateDog1(fido);
// Print Fido's updated information.
print(await dogs());
/*final Database db = await database;
int count =
await db.rawUpdate('UPDATE dogs SET age = ? WHERE id = ?', [35, 0]);
print('updated: $count');
print(await dogs());*/
/*// Delete Fido from the database.
await deleteDog(fido.id);
// Print the list of dogs (empty).
print(await dogs());*/
}
class Dog {
final int id;
final String name;
final int age;
Dog({this.id, this.name, this.age});
Map<String, dynamic> toMap() {
return {
'id': id,
'name': name,
'age': age,
};
}
Map<String, dynamic> toMap1() {
return {
'id': id,
'age': age,
};
}
// Implement toString to make it easier to see information about
// each dog when using the print statement.
@override
String toString() {
return 'Dog{id: $id, name: $name, age: $age}';
}
}
文档中的示例如下所示：
// Update Fido's age and save it to the database.
fido = Dog(
id: fido.id,
name: fido.name,
age: fido.age + 7,
);
await updateDog(fido);
您要么像 chunhunghan 的回答那样使用原始 SQL 查询来处理它，要么 使用 id 查询狗，然后覆盖字段，然后更新。
为什么？
让我们看看您的更新代码：
await updateDog(Dog(id: 0, age: 35));
调用更新行时，将调用 Dog.toMap()，看起来您正在将名称更新为 null。
你可以在这里做你想做的是代码：
Future<Dog> getDog(int id) async {
List<Map> result = await database.query(..... whereArgs: [id]);
if (result.length > 0) {
return new Dog.fromMap(result.first);
}
return null;
}
// Now in code
fido = await getDog(id);
// Update Fido's age and save it to the database.
fido = Dog(
id: fido.id,
name: fido.name,
age: 35, //<--
);
await updateDog(fido);