Conditional logic for generic filter mechanism for Entity Framework

Question

I am looking at implementing a generic filtering and sorting mechanism for my application services.

Having done some research it appears that LINQKit is ideal for this using the predicate builder. I have also found some articles that go into some nice detail in terms of implementation:

• http://www.codeproject.com/Articles/493917/Dynamic-Querying-with-LINQ-to-Entities-and-Express
• http://www.codeproject.com/Tips/582450/Build-Where-Clause-Dynamically-in-Linq

The one thing I have not seen anyone do however is conditional logic of the WHERE clause. Every example I have seen seems to only AND the where conditions.

I am looking for something where I can build up more complex expressions such as:

WHERE ((Field1 = 1 OR Field1 = 2) AND Field2 = 3) OR Field4 = 'A'

Has anyone seen an implementation that adds conditional logic to a generic implementation of filters?

Answer 1

Expression Trees could be your answer. Here are also OR conditions and many more possible. Here my example:

        IQueryable<ENTITY> query = context.ENTITY;
        Expression whereExpression = null;
        ParameterExpression pe = Expression.Parameter(typeof(ENTITY), "name");

        Expression left1 = MemberExpression.Property(pe, "Field1");
        Expression right1 = Expression.Constant(1, typeof(int));
        whereExpression = Expression.And(whereExpression, Expression.Equal(left1, right1));

        Expression left2 = MemberExpression.Property(pe, "Field1");
        Expression right2 = Expression.Constant(2, typeof(int));
        whereExpression = Expression.Or(whereExpression, Expression.Equal(left2, right2));

        Expression left3 = MemberExpression.Property(pe, "Field2");
        Expression right3 = Expression.Constant(3, typeof(int));
        whereExpression = Expression.And(whereExpression, Expression.Equal(left3, right3));

        Expression left4 = MemberExpression.Property(pe, "Field4");
        Expression right4 = Expression.Constant("A", typeof(string));
        whereExpression = Expression.Or(whereExpression, Expression.Equal(left4, right4));

        Expression<Func<ENTITY, bool>> whereCondition = Expression.Lambda<Func<ENTITY, bool>>(whereExpression, new ParameterExpression[] { pe });
        query = query.Where(whereCondition);
        return query.ToList();