C# 如何在实体框架中传递字符串作为泛型数据库集的类型参数?
考虑下面的示例代码,将C#泛型类型作为参数传递的最简洁方法是什么C# 如何在实体框架中传递字符串作为泛型数据库集的类型参数?,c#,entity-framework,reflection,C#,Entity Framework,Reflection,考虑下面的示例代码,将C#泛型类型作为参数传递的最简洁方法是什么 public dynamic MyDbSet(string typeName) { var typeofDbSet = typeof(DbSet<>); Type[] typeArgs = { Type.GetType(typeName) }; var type = typeofDbSet.MakeGenericType(typeArgs); dynamic dbsetOfT = Act
public dynamic MyDbSet(string typeName)
{
var typeofDbSet = typeof(DbSet<>);
Type[] typeArgs = { Type.GetType(typeName) };
var type = typeofDbSet.MakeGenericType(typeArgs);
dynamic dbsetOfT = Activator.CreateInstance(type);
return dbsetOfT;
//Call it
//var notificationTypes = MyDbSet("NotificationType");
//var list = notificationTypes.ToList();
}
公共动态MyDbSet(字符串类型名)
{
var typeofDbSet=typeof(DbSet);
Type[]typeArgs={Type.GetType(typeName)};
var type=typeofDbSet.MakeGenericType(typeArgs);
动态dbsetOfT=Activator.CreateInstance(类型);
返回dbsetOfT;
//叫它
//var notificationTypes=MyDbSet(“NotificationType”);
//var list=notificationTypes.ToList();
}
或者像这样:
public dynamic MyDbSet2(string typeName)
{
var keyValuePairs = new Dictionary<string, dynamic>
{
{nameof(NotificationType), Set<NotificationType>().AsQueryable()}
};
return keyValuePairs[typeName];
//Call it
//var notificationTypes = MyDbSet2("NotificationType");
//var list = notificationTypes.ToList();
}
public DbSet<T> MyDbSet<T>() where T : class
{
return (DbSet<T>)typeof(DbSet<T>).GetConstructor(BindingFlags.NonPublic |
BindingFlags.Instance, null, Type.EmptyTypes, null).Invoke(null);
}
公共动态MyDbSet2(字符串类型名)
{
var keyValuePairs=新字典
{
{nameof(NotificationType),Set().AsQueryable()}
};
返回keyValuePairs[typeName];
//叫它
//var NotificationType=MyDbSet2(“NotificationType”);
//var list=notificationTypes.ToList();
}
Activator.CreateInstance(type)
将失败,因为DbSet
没有公共的无参数构造函数。
除非您确实需要将类型名作为字符串传递,否则最好的方法是创建一个泛型函数,获取构造函数并调用它。它是这样的:
public dynamic MyDbSet2(string typeName)
{
var keyValuePairs = new Dictionary<string, dynamic>
{
{nameof(NotificationType), Set<NotificationType>().AsQueryable()}
};
return keyValuePairs[typeName];
//Call it
//var notificationTypes = MyDbSet2("NotificationType");
//var list = notificationTypes.ToList();
}
public DbSet<T> MyDbSet<T>() where T : class
{
return (DbSet<T>)typeof(DbSet<T>).GetConstructor(BindingFlags.NonPublic |
BindingFlags.Instance, null, Type.EmptyTypes, null).Invoke(null);
}
public DbSet MyDbSet(),其中T:class
{
return(DbSet)typeof(DbSet).GetConstructor(BindingFlags.NonPublic|
BindingFlags.Instance,null,Type.EmptyTypes,null).Invoke(null);
}
然后,您可以通过MyDbSet()调用它
更新:
由于需要传递名称,因此可以执行以下操作:
public dynamic MyDbSet(string typeName)
{
return typeof(DbSet<>).MakeGenericType(Type.GetType(typeName)).
GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance,
null, Type.EmptyTypes, null).Invoke(null);
}
公共动态MyDbSet(字符串类型名)
{
返回typeof(DbSet).MakeGenericType(Type.GetType(typeName))。
GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance,
null,Type.EmptyTypes,null).Invoke(null);
}
然后,您可以通过MyDbSet(“.NotificationType”)
调用它。指定命名空间是必需的,否则Type.GetType
将找不到该类型并返回null
请尝试以下扩展代码:
//Use var list = _context.MyDbSet("ConsoleAppEF.Student").ToList();
public static IQueryable MySet(this SchoolContext context, string typeName)
{
var T = Type.GetType(typeName);
// Get the generic type definition
MethodInfo method = typeof(SchoolContext)
.GetMethod("MySet", BindingFlags.Public | BindingFlags.Instance);
// Build a method with the specific type argument you're interested in
method = method.MakeGenericMethod(T);
return method.Invoke(context, null) as IQueryable;
}
public static IQueryable<T> Set<T>(this SchoolContext context)
{
// Get the generic type definition
MethodInfo method = typeof(SchoolContext)
.GetMethod(nameof(SchoolContext.Set), BindingFlags.Public | BindingFlags.Instance);
// Build a method with the specific type argument you're interested in
method = method.MakeGenericMethod(typeof(T));
return method.Invoke(context, null) as IQueryable<T>;
}
public static IList ToList1(this IQueryable query)
{
var genericToList = typeof(Enumerable).GetMethod("ToList")
.MakeGenericMethod(new Type[] { query.ElementType });
return (IList)genericToList.Invoke(null, new[] { query });
}
使用它:
class Program
{
static void Main(string[] args)
{
Seed();
var _context = new SchoolContext();
var list = _context.MySet("ConsoleAppEF.Student").ToList1();
}
private static void Seed()
{
var _context = new SchoolContext();
var students = new List<Student>
{
new Student{FirstMidName="Carson",LastName="Alexander"},
};
students.ForEach(s => _context.Students.Add(s));
_context.SaveChanges();
}
}
类程序
{
静态void Main(字符串[]参数)
{
种子();
var_context=新学校上下文();
var list=_context.MySet(“ConsoleAppEF.Student”).ToList1();
}
私有静态void Seed()
{
var_context=新学校上下文();
var students=新列表
{
新学生{FirstMidName=“Carson”,LastName=“Alexander”},
};
students.ForEach(s=>_context.students.Add(s));
_SaveChanges();
}
}
我没有,NotificationType,我只有NotificationType字符串_context.MyDbSet(“ConsoleAppEF.Student”).ToList()“”System.Data.Entity.DbSet'不包含“ToList”的定义,但如何使用Linq对Iquerable进行过滤?MySet只返回不能与linq语句一起使用的非泛型Iqueriable。