将表达式转换为Func <Type, bool> 在c＃？

Question

I'm working on a service base application. At the service side, I have to convert Expression to Func<TypeOfEntity,bool> for using in an EntityFramework query.

Type typeofEntity;// we just have type of entity and I could get it from entity name and assembly name
//ExpressionSerializer is in Serialize.Linq
ExpressionSerializer expressionSerializer = new ExpressionSerializer(new JsonSerializer());
Expression expr = expressionSerializer.DeserializeText(stringFromClient);//It's Ok until here
Func<?,bool> func = ?//How can I create Func of typeofEntity and bool
var result = Entities.Something.Where(func);

How can we convert Expression (not Expression<Func<T,bool>> ) to Func<T,bool> ?

Answer 1

You can use the dynamic type to have T resolved at runtime. A class such as this

static class ExpressionRunner
{
    public static IList<T> Run<T>(
        Context context,
        Expression<Func<T, bool>> expression)
        where T : class
    {
        var result = context
            .Set<T>()
            .Where(expression);

        return result.ToList();
    }

}

Can run the Expression against the Context

Expression expr = expressionSerializer.DeserializeText(stringFromClient);
var result = ExpressionRunner.Run(Entities, expr as dynamic);

Note that the return type is also dynamic so it would be advisable to have this Run method at the top of the call chain to maximise performance - ie Run should return void and all the processing should be nested inside of Run .