使用运行时解析的类型调用System.Linq.Queryable方法
我正在构建一个基于LINQ的查询生成器 其中一个特性是能够将任意服务器端投影指定为查询定义的一部分。例如:使用运行时解析的类型调用System.Linq.Queryable方法,linq,generics,reflection,dynamic,c#-4.0,Linq,Generics,Reflection,Dynamic,C# 4.0,我正在构建一个基于LINQ的查询生成器 其中一个特性是能够将任意服务器端投影指定为查询定义的一部分。例如: class CustomerSearch : SearchDefinition<Customer> { protected override Expression<Func<Customer, object>> GetProjection() { return x => new
class CustomerSearch : SearchDefinition<Customer>
{
protected override Expression<Func<Customer, object>> GetProjection()
{
return x => new
{
Name = x.Name,
Agent = x.Agent.Code
Sales = x.Orders.Sum(o => o.Amount)
};
}
}
为了返回投影查询,我希望能够这样做(事实上,这在几乎相同的概念证明中起作用):
有人知道更好的方法吗?
更新:
动态
失败的原因是匿名类型被定义为内部
。这就是为什么它使用概念验证项目工作的原因,在这个项目中,所有东西都在同一个组件中
我不介意。我仍然希望找到一种更干净的方法来找到正确的
查询表。选择重载。这是我的测试。这是一个Northwind数据库,对我来说很好
static void Main(string[] args)
{
var dc = new NorthwindDataContext();
var source = dc.Categories;
Expression<Func<Category, object>> expr =
c => new
{
c.CategoryID,
c.CategoryName,
};
var oldParameter = expr.Parameters.Single();
var parameter = Expression.Parameter(oldParameter.Type, oldParameter.Name);
var body = expr.Body;
body = RebindParameter(body, oldParameter, parameter);
Console.WriteLine("Parameter Type: {0}", parameter.Type);
Console.WriteLine("Body Type: {0}", body.Type);
var newExpr = Expression.Lambda(body, parameter);
Console.WriteLine("Old Expression Type: {0}", expr.Type);
Console.WriteLine("New Expression Type: {0}", newExpr.Type);
var query = Queryable.Select(source, (dynamic)newExpr);
Console.WriteLine(query);
foreach (var item in query)
{
Console.WriteLine(item);
Console.WriteLine("\t{0}", item.CategoryID.GetType());
Console.WriteLine("\t{0}", item.CategoryName.GetType());
}
Console.Write("Press any key to continue . . . ");
Console.ReadKey(true);
Console.WriteLine();
}
static Expression RebindParameter(Expression expr, ParameterExpression oldParam, ParameterExpression newParam)
{
switch (expr.NodeType)
{
case ExpressionType.Parameter:
var parameterExpression = expr as ParameterExpression;
return (parameterExpression.Name == oldParam.Name)
? newParam
: parameterExpression;
case ExpressionType.MemberAccess:
var memberExpression = expr as MemberExpression;
return memberExpression.Update(
RebindParameter(memberExpression.Expression, oldParam, newParam));
case ExpressionType.AndAlso:
case ExpressionType.OrElse:
case ExpressionType.Equal:
case ExpressionType.NotEqual:
case ExpressionType.LessThan:
case ExpressionType.LessThanOrEqual:
case ExpressionType.GreaterThan:
case ExpressionType.GreaterThanOrEqual:
var binaryExpression = expr as BinaryExpression;
return binaryExpression.Update(
RebindParameter(binaryExpression.Left, oldParam, newParam),
binaryExpression.Conversion,
RebindParameter(binaryExpression.Right, oldParam, newParam));
case ExpressionType.New:
var newExpression = expr as NewExpression;
return newExpression.Update(
newExpression.Arguments
.Select(arg => RebindParameter(arg, oldParam, newParam)));
case ExpressionType.Call:
var methodCallExpression = expr as MethodCallExpression;
return methodCallExpression.Update(
RebindParameter(methodCallExpression.Object, oldParam, newParam),
methodCallExpression.Arguments
.Select(arg => RebindParameter(arg, oldParam, newParam)));
default:
return expr;
}
}
解决方法非常简单,令人心痛:
[assembly: InternalsVisibleTo("My.Search.Lib.Assembly")]
调用ParameterRebinder.ReplaceParameter
真的有必要吗?表达式主体已具有正确的类型,因此重建表达式时,它将具有正确的类型。我自己的测试似乎在这里工作。@JeffM:调用是替换匿名类型初始值设定项中原始lambda表达式中的参数所必需的,否则您将从作用域“”中引用类型为“Customer”的变量“x”,但它未定义
。我可能应该创建一个完整的测试用例,因为它在一个概念验证项目中也适用于我。我的测试只是在一个新的lambda表达式中重用现有的参数和主体(并且有效)。做同样的工作对你有帮助吗?@JeffM:你能发布你的测试吗?记住投影是在一个子类中定义的。@Jeff我删除了RebindParameter的东西,这一部分现在更简单了,但我仍然得到相同的错误。“我将尝试创建一个完整的复制品。@杰夫:我发现了为什么它对你有效而对我无效。检查我的最新更新。@Diego:好的,很好。但一般来说,只要可以确定运行时类型,动态调度就会正常工作。如果表达式中有任何变量被声明为动态变量,则在运行时解决所有问题。@JeffM:不幸的是,后期绑定上下文中的Cast()
就像Cast
:它不允许我在投影类型的属性上添加OrderBy
(这就是我做整个表达式的原因。Lambda hack)@JeffM:看看我的解决方案是什么:-)如果你没有将此标记为社区wiki,我仍然会投票支持你的努力,并让我走上正确的道路。谢谢
Microsoft.CSharp.RuntimeBinder.RuntimeBinderException:
The best overloaded method match for
'System.Linq.Queryable.Select<Customer,object>(System.Linq.IQueryable<Customer>,
System.Linq.Expressions.Expression<System.Func<Customer,object>>)'
has some invalid arguments
at CallSite.Target(Closure , CallSite , Type , IQueryable`1 , Object )
at System.Dynamic.UpdateDelegates.UpdateAndExecute3[T0,T1,T2,TRet]
(CallSite site, T0 arg0, T1 arg1, T2 arg2)
at SearchDefinition`1.Transform(IQueryable source) in ...
var genericSelectMethod = typeof(Queryable).GetMethods().Single(
x => x.Name == "Select" &&
x.GetParameters()[1].ParameterType.GetGenericArguments()[0]
.GetGenericArguments().Length == 2);
var selectMethod = genericSelectMethod.MakeGenericMethod(source.ElementType,
projectionBody.Type);
return (IQueryable)selectMethod.Invoke(null, new object[]{ source, projection });
static void Main(string[] args)
{
var dc = new NorthwindDataContext();
var source = dc.Categories;
Expression<Func<Category, object>> expr =
c => new
{
c.CategoryID,
c.CategoryName,
};
var oldParameter = expr.Parameters.Single();
var parameter = Expression.Parameter(oldParameter.Type, oldParameter.Name);
var body = expr.Body;
body = RebindParameter(body, oldParameter, parameter);
Console.WriteLine("Parameter Type: {0}", parameter.Type);
Console.WriteLine("Body Type: {0}", body.Type);
var newExpr = Expression.Lambda(body, parameter);
Console.WriteLine("Old Expression Type: {0}", expr.Type);
Console.WriteLine("New Expression Type: {0}", newExpr.Type);
var query = Queryable.Select(source, (dynamic)newExpr);
Console.WriteLine(query);
foreach (var item in query)
{
Console.WriteLine(item);
Console.WriteLine("\t{0}", item.CategoryID.GetType());
Console.WriteLine("\t{0}", item.CategoryName.GetType());
}
Console.Write("Press any key to continue . . . ");
Console.ReadKey(true);
Console.WriteLine();
}
static Expression RebindParameter(Expression expr, ParameterExpression oldParam, ParameterExpression newParam)
{
switch (expr.NodeType)
{
case ExpressionType.Parameter:
var parameterExpression = expr as ParameterExpression;
return (parameterExpression.Name == oldParam.Name)
? newParam
: parameterExpression;
case ExpressionType.MemberAccess:
var memberExpression = expr as MemberExpression;
return memberExpression.Update(
RebindParameter(memberExpression.Expression, oldParam, newParam));
case ExpressionType.AndAlso:
case ExpressionType.OrElse:
case ExpressionType.Equal:
case ExpressionType.NotEqual:
case ExpressionType.LessThan:
case ExpressionType.LessThanOrEqual:
case ExpressionType.GreaterThan:
case ExpressionType.GreaterThanOrEqual:
var binaryExpression = expr as BinaryExpression;
return binaryExpression.Update(
RebindParameter(binaryExpression.Left, oldParam, newParam),
binaryExpression.Conversion,
RebindParameter(binaryExpression.Right, oldParam, newParam));
case ExpressionType.New:
var newExpression = expr as NewExpression;
return newExpression.Update(
newExpression.Arguments
.Select(arg => RebindParameter(arg, oldParam, newParam)));
case ExpressionType.Call:
var methodCallExpression = expr as MethodCallExpression;
return methodCallExpression.Update(
RebindParameter(methodCallExpression.Object, oldParam, newParam),
methodCallExpression.Arguments
.Select(arg => RebindParameter(arg, oldParam, newParam)));
default:
return expr;
}
}
var query = Queryable.Select(source, expr).Cast<dynamic>();
Console.WriteLine(query);
foreach (var item in query)
{
Console.WriteLine(item);
Console.WriteLine("\t{0}", item.CategoryID.GetType());
Console.WriteLine("\t{0}", item.CategoryName.GetType());
}
[assembly: InternalsVisibleTo("My.Search.Lib.Assembly")]