如何在 EF Core 3 中动态获取 DbSet？
How to get DbSet dynamically in EF Core 3?
您好，我正在尝试这样做：
我有更多 classes，用户可以在其中存储文件 - 这些文件的路径以 JSON 格式存储在数据库中，文件存储在名为 class 的文件夹中（因此，当 class 名称为 Foo 时，文件将存储在 Files/Foo/Foobar.pdf 中）。
我有一个控制器，我将路径发送到应该删除的文件。在这里我无法解决问题，我还需要从数据库中删除此文件路径，但我找不到如何动态获取 DbSet。
我在这里搜索了很多问题，但几乎每次都能找到 DbContext.Set()，但 ASP.NET CORE 3.0 中不存在此方法。你能帮我看看怎么做吗？
这是我的控制器：
[HttpGet]
public JsonResult DeleteFile(string id)
{
KeyValuePair<string, string> message;
if (!string.IsNullOrEmpty(id))
{
string filePath = Uri.UnescapeDataString(id);
if (filePath.CheckIfExists())
{
string nameOfInstance = filePath.GetNumberAccordingToFileName();
string tableName = filePath[1..(filePath.IndexOf('/', 1) - 1)];
Type type = Assembly.GetExecutingAssembly()
.GetTypes()
.FirstOrDefault(t => t.Name.Equals(tableName,StringComparison.OrdinalIgnoreCase));
if(type.IsClass)
{
var entity = db.GetDbSet(Activator.CreateInstance(type)); //this is not working
var item = entity.GetDataFromDbase(nameOfInstance,1,0,"Number","ASC","Number",false,out int filteredResultsCount, out int totalResultsCount, false).FirstOrDefault(); //find the item
item = item.DeleteFileFromItem(User.Identity.Name, filePath);
db.Update(item);
var result = db.SaveChanges();
if (result > 0)
{
if (filePath.DeleteFile())
{
message = new KeyValuePair<string, string>(MessagesHandler.Success, $"File {filePath.Substring(filePath.LastIndexOf("/"))} was successfully deleted.");
return Json(new
{
status = true,
message
});
}
else
{
message = new KeyValuePair<string, string>(MessagesHandler.Error, $"File {filePath.Substring(filePath.LastIndexOf("/"))} was not deleted.");
return Json(new
{
status = false,
message
});
}
} //if the changes were not made in DB
message = new KeyValuePair<string, string>(MessagesHandler.Error, $"File {filePath.Substring(filePath.LastIndexOf("/"))} was deleted, error in DB");
return Json(new
{
status = false,
message
});
}
}//error message when file not found
message = new KeyValuePair<string, string>(MessagesHandler.Error, $"File {filePath} not found.");
return Json(new
{
status = false,
message
});
}//error message when filename is empty
message = new KeyValuePair<string, string>(MessagesHandler.Error, $"Field ID cannot be empty");
return Json(new
{
status = false,
message
});
}
这是方法 GetDbSet:
public static Microsoft.EntityFrameworkCore.DbSet<TEntity> GetDbSet<TEntity>(this DataContext db, TEntity t) where TEntity : class
{
Type type = t.GetType();
return (Microsoft.EntityFrameworkCore.DbSet<TEntity>)typeof(DataContext).GetMethod(nameof(DataContext.Set)).MakeGenericMethod(type).Invoke(db, null);
}
这里我遇到了这个异常：
System.InvalidCastException
HResult=0x80004002
Message=Unable to cast object of type 'Microsoft.EntityFrameworkCore.Internal.InternalDbSet1[SmartLab_System.Models.TestRequirement]' to type 'Microsoft.EntityFrameworkCore.DbSet1[System.Object]'.
方法 GetDataFromDbase:
public static List<T> GetDataFromDbase<T>(this IEnumerable<T> entity, string searchBy, int take, int skip, string sortBy,
string sortDir, string columnName, bool showDeactivatedItems, out int filteredResultsCount, out int totalResultsCount, bool countResult = true) where T : class
{
IEnumerable<T> helper;
if (!String.IsNullOrEmpty(searchBy))//if any string to search was given
{
//find the properties we would like to search in
var properties = typeof(T).GetProperties()
.Where(x => x.CanRead && columnName.Contains(x.Name, StringComparison.InvariantCultureIgnoreCase) && columnName.Length == x.Name.Length)
.Select(x => x.GetMethod)
.Where(x => !x.IsStatic);
//.ToList();
//list of all items where searched value was found
helper = entity.GetActiveItems(showDeactivatedItems)
.Where(m => properties
.Select(p => p.Invoke(m, null)?.ToString() ?? string.Empty)
.Any(a => a.ToString().Contains(searchBy, StringComparison.InvariantCultureIgnoreCase)) == true);
//.ToList();
}
else//if no string to search was given
{
helper = entity.GetActiveItems(showDeactivatedItems); //all items
}
List<T> result;
if (take < 1)
{
result = helper
.OrderBy(sortBy + " " + sortDir)
.ToList();
}
else
{
result = helper
.OrderBy(sortBy + " " + sortDir)
.Skip(skip)
.Take(take)
.ToList();
}
if (countResult)
{
filteredResultsCount = helper.Count();//how many items is sent
totalResultsCount = entity.Count(); //how many items is in database
}
else
{
filteredResultsCount = 0;//how many items is sent
totalResultsCount = 0;
}
return result;
}
除了打电话db.GetDbSet(type)我也试过db.GetDbSet(Activator.CreateInstance(type))但没用。
我在评论（）中发布的link将为您检索集合，但您无法对其进行操作，因为它是IQueryable类型而不是[=13] =].
我认为可以通过在实体上使用简单的开关和通用接口来为您提供更好的解决方案。只要您的数据库中没有 100 多个表，这将非常容易维护。
var entityType = "Drawer";
var pathToRemove = "somepath";
var id = 1;
// get queryable based on entity type
IQueryable<IHasFiles> queryable = entityType switch
{
"Drawer" => context.Set<Drawer>().OfType<IHasFiles>(),
"Bookshelf" => context.Set<Bookshelf>().OfType<IHasFiles>(),
_ => throw new ArgumentException("Unknown entity type", nameof(entityType))
};
// pick the item and include all files
var item = await queryable.Where(i => i.Id == id).Include(i => i.Files).SingleAsync();
// pick the correct file
var file = item.Files.Single(f => f.Path == pathToRemove);
// remove it
item.Files.Remove(file);
// save changes to db
await context.SaveChangesAsync();
实体定义如下
public interface IHasFiles
{
int Id { get; }
ICollection<File> Files { get; set; }
}
public class File
{
public int Id { get; set; }
public string Path { get; set; }
}
public class Drawer : IHasFiles
{
public int Id { get; set; }
public ICollection<File> Files { get; set; }
}
public class Bookshelf : IHasFiles
{
public int Id { get; set; }
public ICollection<File> Files { get; set; }
}
您好，我正在尝试这样做：
我有更多 classes，用户可以在其中存储文件 - 这些文件的路径以 JSON 格式存储在数据库中，文件存储在名为 class 的文件夹中（因此，当 class 名称为 Foo 时，文件将存储在 Files/Foo/Foobar.pdf 中）。
我有一个控制器，我将路径发送到应该删除的文件。在这里我无法解决问题，我还需要从数据库中删除此文件路径，但我找不到如何动态获取 DbSet。
我在这里搜索了很多问题，但几乎每次都能找到 DbContext.Set()，但 ASP.NET CORE 3.0 中不存在此方法。你能帮我看看怎么做吗？
这是我的控制器：
[HttpGet]
public JsonResult DeleteFile(string id)
{
KeyValuePair<string, string> message;
if (!string.IsNullOrEmpty(id))
{
string filePath = Uri.UnescapeDataString(id);
if (filePath.CheckIfExists())
{
string nameOfInstance = filePath.GetNumberAccordingToFileName();
string tableName = filePath[1..(filePath.IndexOf('/', 1) - 1)];
Type type = Assembly.GetExecutingAssembly()
.GetTypes()
.FirstOrDefault(t => t.Name.Equals(tableName,StringComparison.OrdinalIgnoreCase));
if(type.IsClass)
{
var entity = db.GetDbSet(Activator.CreateInstance(type)); //this is not working
var item = entity.GetDataFromDbase(nameOfInstance,1,0,"Number","ASC","Number",false,out int filteredResultsCount, out int totalResultsCount, false).FirstOrDefault(); //find the item
item = item.DeleteFileFromItem(User.Identity.Name, filePath);
db.Update(item);
var result = db.SaveChanges();
if (result > 0)
{
if (filePath.DeleteFile())
{
message = new KeyValuePair<string, string>(MessagesHandler.Success, $"File {filePath.Substring(filePath.LastIndexOf("/"))} was successfully deleted.");
return Json(new
{
status = true,
message
});
}
else
{
message = new KeyValuePair<string, string>(MessagesHandler.Error, $"File {filePath.Substring(filePath.LastIndexOf("/"))} was not deleted.");
return Json(new
{
status = false,
message
});
}
} //if the changes were not made in DB
message = new KeyValuePair<string, string>(MessagesHandler.Error, $"File {filePath.Substring(filePath.LastIndexOf("/"))} was deleted, error in DB");
return Json(new
{
status = false,
message
});
}
}//error message when file not found
message = new KeyValuePair<string, string>(MessagesHandler.Error, $"File {filePath} not found.");
return Json(new
{
status = false,
message
});
}//error message when filename is empty
message = new KeyValuePair<string, string>(MessagesHandler.Error, $"Field ID cannot be empty");
return Json(new
{
status = false,
message
});
}
这是方法 GetDbSet:
public static Microsoft.EntityFrameworkCore.DbSet<TEntity> GetDbSet<TEntity>(this DataContext db, TEntity t) where TEntity : class
{
Type type = t.GetType();
return (Microsoft.EntityFrameworkCore.DbSet<TEntity>)typeof(DataContext).GetMethod(nameof(DataContext.Set)).MakeGenericMethod(type).Invoke(db, null);
}
这里我遇到了这个异常：
System.InvalidCastException HResult=0x80004002 Message=Unable to cast object of type 'Microsoft.EntityFrameworkCore.Internal.InternalDbSet
1[SmartLab_System.Models.TestRequirement]' to type 'Microsoft.EntityFrameworkCore.DbSet1[System.Object]'.
方法 GetDataFromDbase:
public static List<T> GetDataFromDbase<T>(this IEnumerable<T> entity, string searchBy, int take, int skip, string sortBy,
string sortDir, string columnName, bool showDeactivatedItems, out int filteredResultsCount, out int totalResultsCount, bool countResult = true) where T : class
{
IEnumerable<T> helper;
if (!String.IsNullOrEmpty(searchBy))//if any string to search was given
{
//find the properties we would like to search in
var properties = typeof(T).GetProperties()
.Where(x => x.CanRead && columnName.Contains(x.Name, StringComparison.InvariantCultureIgnoreCase) && columnName.Length == x.Name.Length)
.Select(x => x.GetMethod)
.Where(x => !x.IsStatic);
//.ToList();
//list of all items where searched value was found
helper = entity.GetActiveItems(showDeactivatedItems)
.Where(m => properties
.Select(p => p.Invoke(m, null)?.ToString() ?? string.Empty)
.Any(a => a.ToString().Contains(searchBy, StringComparison.InvariantCultureIgnoreCase)) == true);
//.ToList();
}
else//if no string to search was given
{
helper = entity.GetActiveItems(showDeactivatedItems); //all items
}
List<T> result;
if (take < 1)
{
result = helper
.OrderBy(sortBy + " " + sortDir)
.ToList();
}
else
{
result = helper
.OrderBy(sortBy + " " + sortDir)
.Skip(skip)
.Take(take)
.ToList();
}
if (countResult)
{
filteredResultsCount = helper.Count();//how many items is sent
totalResultsCount = entity.Count(); //how many items is in database
}
else
{
filteredResultsCount = 0;//how many items is sent
totalResultsCount = 0;
}
return result;
}
除了打电话db.GetDbSet(type)我也试过db.GetDbSet(Activator.CreateInstance(type))但没用。
我在评论（IQueryable类型而不是[=13] =].
我认为可以通过在实体上使用简单的开关和通用接口来为您提供更好的解决方案。只要您的数据库中没有 100 多个表，这将非常容易维护。
var entityType = "Drawer";
var pathToRemove = "somepath";
var id = 1;
// get queryable based on entity type
IQueryable<IHasFiles> queryable = entityType switch
{
"Drawer" => context.Set<Drawer>().OfType<IHasFiles>(),
"Bookshelf" => context.Set<Bookshelf>().OfType<IHasFiles>(),
_ => throw new ArgumentException("Unknown entity type", nameof(entityType))
};
// pick the item and include all files
var item = await queryable.Where(i => i.Id == id).Include(i => i.Files).SingleAsync();
// pick the correct file
var file = item.Files.Single(f => f.Path == pathToRemove);
// remove it
item.Files.Remove(file);
// save changes to db
await context.SaveChangesAsync();
实体定义如下
public interface IHasFiles
{
int Id { get; }
ICollection<File> Files { get; set; }
}
public class File
{
public int Id { get; set; }
public string Path { get; set; }
}
public class Drawer : IHasFiles
{
public int Id { get; set; }
public ICollection<File> Files { get; set; }
}
public class Bookshelf : IHasFiles
{
public int Id { get; set; }
public ICollection<File> Files { get; set; }
}