如何动态创建Expression< Func< MyClass,bool>>谓词? [英] How do I dynamically create an Expression<Func<MyClass, bool>> predicate?
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问题描述
我将如何使用表达式树动态创建一个看起来像...的谓词.
How would I go about using an Expression Tree to dynamically create a predicate that looks something like...
(p.Length== 5) && (p.SomeOtherProperty == "hello")
这样我就可以将谓词粘贴到这样的lambda表达式中...
So that I can stick the predicate into a lambda expression like so...
q.Where(myDynamicExpression)...
我只需要指出正确的方向.
I just need to be pointed in the right direction.
更新:抱歉,我没有提到我希望谓词具有上述多个条件的事实.抱歉造成混乱.
Update: Sorry folks, I left out the fact that I want the predicate to have multiple conditions as above. Sorry for the confusion.
推荐答案
原始
像这样:
var param = Expression.Parameter(typeof(string), "p");
var len = Expression.PropertyOrField(param, "Length");
var body = Expression.Equal(
len, Expression.Constant(5));
var lambda = Expression.Lambda<Func<string, bool>>(
body, param);
已更新
re (p.Length== 5) && (p.SomeOtherProperty == "hello")
:
var param = Expression.Parameter(typeof(SomeType), "p");
var body = Expression.AndAlso(
Expression.Equal(
Expression.PropertyOrField(param, "Length"),
Expression.Constant(5)
),
Expression.Equal(
Expression.PropertyOrField(param, "SomeOtherProperty"),
Expression.Constant("hello")
));
var lambda = Expression.Lambda<Func<SomeType, bool>>(body, param);
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