Converting a Linq expression tree that relies on SqlMethods.Like() for use with the Entity Framework

Question

I recently switched from using Linq to Sql to the Entity Framework. One of the things that I've been really struggling with is getting a general purpose IQueryable extension method that was built for Linq to Sql to work with the Entity Framework. This extension method has a dependency on the Like() method of SqlMethods, which is Linq to Sql specific. What I really like about this extension method is that it allows me to dynamically construct a Sql Like statement on any object at runtime, by simply passing in a property name (as string) and a query clause (also as string). Such an extension method is very convenient for using grids like flexigrid or jqgrid. Here is the Linq to Sql version (taken from this tutorial: http://www.codeproject.com/KB/aspnet/MVCFlexigrid.aspx ):

    public static IQueryable<T> Like<T>(this IQueryable<T> source,
                  string propertyName, string keyword)
    {
        var type = typeof(T);
        var property = type.GetProperty(propertyName);
        var parameter = Expression.Parameter(type, "p");
        var propertyAccess = Expression.MakeMemberAccess(parameter, property);
        var constant = Expression.Constant("%" + keyword + "%");
        var like = typeof(SqlMethods).GetMethod("Like",
                   new Type[] { typeof(string), typeof(string) });
        MethodCallExpression methodExp =
              Expression.Call(null, like, propertyAccess, constant);
        Expression<Func<T, bool>> lambda =
              Expression.Lambda<Func<T, bool>>(methodExp, parameter);
        return source.Where(lambda);
    }

With this extension method, I can simply do the following:

someList.Like("FirstName", "mike");

or

anotherList.Like("ProductName", "widget");

Is there an equivalent way to do this with Entity Framework?

Thanks in advance.

Answer 1

The SQL method PATINDEX provides the same functionality as LIKE. Therefore, you can use the SqlFunctions.PatIndex method.

.Where(x => SqlFunctions.PatIndex("%123%ABC", x.MySearchField) > 0)

or

var miSqlPatIndex = typeof(SqlFunctions).GetMethod(
    "PatIndex", 
    BindingFlags.Public | BindingFlags.Static | BindingFlags.IgnoreCase, 
    null, 
    new Type[] { typeof(string), typeof(string) }, 
    null);                        
expr = Expression.GreaterThan(
    Expression.Call(
        miSqlPatIndex, 
        new Expression[] { Expression.Constant("%123%ABC"), MySearchField }),
        Expression.Convert(Expression.Constant(0), typeof(int?)));

Answer 2

I was able to find a good solution here: http://www.codeproject.com/KB/aspnet/AspNetMVCandJqGrid.aspx

It essentially uses the "Contains" method of the string class instead of the Like method of the SqlMethods class.

Expression condition = Expression.Call(memberAccess, typeof(string).GetMethod("Contains"), Expression.Constant(keyword));

Answer 3

You could consider looking at this:

http://naspinski.net/post/Universal-IQueryable-Search-Version-2-with-Reflection.aspx