获取数据的表达式查询的动态创建我想创建Expression
类型的查询会从实体框架的实体的一些列。从实体框架
假设我们有两个类是这样的:
public class Parent
{
public int Id { get; set; }
public string Name { get; set; }
public Child MyChild { get; set; }
}
public class Child
{
public int Id { get; set; }
public string Name { get; set; }
}
而且我们有Parent
的IQueryable
列表:
var q = new List<Parent>()
{
new Parent {Id = 1, Name = "a", Number = 1, MyChild=new Child{Id=11,Name="Child_a",Number=2}},
new Parent {Id = 2, Name = "b", Number = 1, MyChild=new Child{Id=22,Name="Child_b",Number=2}},
new Parent {Id = 3, Name = "c", Number = 1, MyChild=new Child{Id=33,Name="Child_c",Number=2}},
}.AsQueryable();
我希望该用户决定他们得到的q
这些属性的列表。例如,用户确定他需要Parent.Name
和Parent.MyChils.Name
。所以,我应该给用户这样的匿名类型的列表:
{"a","Child_a"}
{"b","Child_b"}
{"c","Child_c"}
如果Parent
实体不含有任何外键属性(在这个例子中MyChild
属性)它是那么容易创造一个表达的属性,动态地获取Parent
的一些属性。我有得到的Person
某些属性没有它MyChild
属性的代码:
var columns = new List<string> { "Id", "Name" };
var xParam = Expression.Parameter(typeof(Parent), "x");
var sourceProperties = columns.ToDictionary(name => name,
name => q.ElementType.GetProperty(name));
var dynamicType = LinqRuntimeTypeBuilder.GetDynamicType(sourceProperties.Values);
var bindings =
dynamicType.GetFields()
.Select(p => Expression.Bind(p, Expression.Property(xParam, sourceProperties[p.Name])))
.OfType<MemberBinding>();
var newExpr = Expression.New(dynamicType.GetConstructor(Type.EmptyTypes));
Expression selector = Expression.Lambda(Expression.MemberInit(
Expression.New(dynamicType.GetConstructor(Type.EmptyTypes)), bindings), xParam);
var body = Expression.MemberInit(newExpr, bindings);
var lambda = Expression.Lambda<Func<Parent, dynamic>>(body, xParam);
var t = q.Select(lambda);
(使用2种方法在这里:)
public static Type GetDynamicType2(Dictionary<string, Type> fields)
{
if (null == fields)
throw new ArgumentNullException("fields");
if (0 == fields.Count)
throw new ArgumentOutOfRangeException("fields", "fields must have at least 1 field definition");
try
{
Monitor.Enter(builtTypes);
string className = "MyDynamicType";
if (builtTypes.ContainsKey(className))
return builtTypes[className];
TypeBuilder typeBuilder = moduleBuilder.DefineType(className,
TypeAttributes.Public | TypeAttributes.Class | TypeAttributes.Serializable);
foreach (var field in fields)
typeBuilder.DefineField(field.Key, field.Value, FieldAttributes.Public);
builtTypes[className] = typeBuilder.CreateType();
return builtTypes[className];
}
catch (Exception ex)
{
}
finally
{
Monitor.Exit(builtTypes);
}
return null;
}
public static Type GetDynamicType(IEnumerable<PropertyInfo> fields)
{
return GetDynamicType(fields.ToDictionary(f => f.Name, f => f.PropertyType));
}
但我仍不能得到MyChild
属性的内部属性的Parent
。
如何做到这一点?