考虑以下示例代码,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 = Activator.CreateInstance(type);
return dbsetOfT;
//Call it
//var notificationTypes = MyDbSet("NotificationType");
//var list = notificationTypes.ToList();
}
或者类似这样的东西:
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();
}
答案 0 :(得分:1)
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称作为字符串传递,否则执行此操作的最佳方法是创建泛型函数,获取构造函数并调用它。会是这样的:
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);
}
然后,您将通过MyDbSet<NotificationType>()
更新:
由于必须传递名称,因此您可以执行以下操作:
public dynamic MyDbSet(string typeName)
{
return typeof(DbSet<>).MakeGenericType(Type.GetType(typeName)).
GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance,
null, Type.EmptyTypes, null).Invoke(null);
}
然后,您将通过MyDbSet("<namespace>.NotificationType")
进行调用。需要指定名称空间,因为否则Type.GetType
将找不到类型并返回null
答案 1 :(得分:1)
尝试使用此扩展代码:
//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 });
}
示例DbContext:
public class SchoolContext : DbContext
{
public SchoolContext() : base("SchoolContext")
{
}
public DbSet<Student> Students { get; set; }
public virtual new DbSet<TEntity> MySet<TEntity>() where TEntity : BaseEntity
{
return base.Set<TEntity>();
}
}
示例实体:
public class Student : BaseEntity
{
public string LastName { get; set; }
public string FirstMidName { get; set; }
}
public class BaseEntity
{
public int Id { get; set; }
}
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();
}
}