Question

I was attempting to dynamically create a Where predicate for a LINQ2SQL query:

...Where(SqlMethods.Like(r.Name, '%A%') ||          SqlMethods.Like(r.Name, '%B%') ||          SqlMethods.Like(r.Name, '%C%') || ...) 

A, B, C, etc. come from some array. So I tried the following:

var roleExpression = Expression.Parameter(typeof(Role), r); var nameExpression = Expression.Property(roleExpression, 'Name'); var termExpression = Expression.Constant('%' + term[i] + '%'); var likeExpression = Expression.Call(     typeof(SqlMethods), 'Like',     new[] { typeof(string), typeof(string) }, nameExpression, termExpression); 

However, the last line fails with the message No method ‘Like’ on type ‘System.Data.Linq.SqlClient.SqlMethods’ is compatible with the supplied arguments.

So I tried the following line:

var likeExpression = Expression.Call(null,     typeof(SqlMethods).GetMethod('Like', new[] { typeof(string), typeof(string) }),     nameExpression, searchTermExpression) 

This works. However, I don’t understand what the difference is between these two lines. In my opinion they should deliver the same result.

Could anyone explain this?

Kind regards,
Ronald Wildenberg

Answer 1

I believe that the Type[] argument is for generic type parameters – i.e. you were trying to call:

SqlMethods.Like<string,string>(...); // note the <string,string> 

Try passing an empty Type[].

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Edit re the confusion (comments); my point is: you shouldn’t be specifying anything for the Type[] argument. Either an empty array or null would do; for example:

var likeExpression = Expression.Call(     typeof(SqlMethods), 'Like', null, nameExpression, termExpression);