需要帮助转换“Any（）” lambda到表达式树 [英] Need help converting "Any()" lambda to an expression tree

问题描述

请考虑以下几点。 （这是有效的，但是我需要帐号作为一个字符串传递。帐户是帐户列表）

Consider the following. (which works, but I need Accounts to be passed in as a string. Accounts is list of Account)

repo = repo.Where(x => x.Accounts.Any(p => p.Id == 1));

这是我到目前为止，但我似乎无法将它们连线在一起。

Here is what I have so far, but I can't seem to wire them together at the end.

        var parameterExp = Expression.Parameter(typeof(Car), "x");
        Expression propertyExp = Expression.Property(parameterExp, "Accounts");

        //Type elementType = propertyExp.Type.GetGenericArguments()[0];

        MethodInfo AnyMethod = typeof(Enumerable).GetMethods(BindingFlags.Public | BindingFlags.Static).First(m => m.Name == "Any");

        var parameterExp2 = Expression.Parameter(typeof(Car), "p");

        var idExpr = Expression.PropertyOrField(parameterExp2, "Id");

        MethodInfo method = typeof(long).GetMethod("Equals", new[] { typeof(long) });
        var _relatedToId = Expression.Constant(relatedToId, typeof(long));
        var equalsMethodExp = Expression.Call(idExpr, method, _relatedToId);

        // This is where it breaks. I can't seem to wire it together correctly.
        var call = Expression.Call(
            AnyMethod,
            propertyExp,
            equalsMethodExp);

        Expression<Func<Car, bool>> predicate = Expression.Lambda<Func<Car, bool>>(call, parameterExp);

        // Need to return x => x.Accounts.Any(p => p.Id.Equals(1))
        return predicate;

提前感谢

推荐答案

您有几个错误：

• 首先，取消注释下面的

• Firstly, uncomment line below

Type elementType = propertyExp.Type.GetGenericArguments()[0];

其次，您不正确地检索 MethodInfo 为任何。您需要包含两个参数（source，func）的信息，您需要获取任何任何< Account> 的封闭类型，而不是打开 Any< < / code>：

Secondly, you don't correctly retrieve MethodInfo for Any. You need info that contains two parameters (source, func) and you need to get the closed type of Any Any<Account> not the open Any<>:

MethodInfo AnyMethod = typeof(Enumerable)
                       .GetMethods(BindingFlags.Public | BindingFlags.Static)
                       .First(m => m.Name == "Any" && m.GetParameters().Length > 1);
var closedAnyMethod = AnyMethod.MakeGenericMethod(elementType);

第三， parameterExp2 。它应该是帐户不汽车：

var parameterExp2 = Expression.Parameter(elementType, "p");

第四，你应该转换一个 MethodCallExpression for 等于方法到lambda表达式。您不能直接将等于'调用表达式传递给任何，因为任何获取 Func< T，bool> 作为参数：

Fourthly, you should convert a MethodCallExpression for Equals method to lambda expression. You cannot directly pass Equals' call expression to Any because Any gets Func<T, bool> as parameter:

var equalsMethodExp = Expression.Call(idExpr, method, _relatedToId);
var lambdaAny = Expression.Lambda(typeof(Func<,>).MakeGenericType(elementType, typeof(bool)), equalsMethodExp, parameterExp2);

最后，您只需要调用另一个覆盖 Expression即可。调用：

var call = Expression.Call(
        closedAnyMethod,
        propertyExp,
        lambdaAny);

让我知道如果你想得到完整的代码。

Let me know if you want to get the complete code.

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