Question

Hi i am using entity framework and LinQ. I have a table objects called users . i have a list called userids. i have to find all users where ids contains in the string. I have to do following operations …

select * from users where userid in (userids);

I tried to solve this like this

var u = context.users.Where(o=> usersid.Contains(o=> o.userid)).Select(o=> o);

but it gives compilation error. how to solve this ?

Answer 1

Try to use this :

protected Expression<Func<TElement, bool>> BuildContainsExpression<TElement, TValue>(Expression<Func<TElement, TValue>> valueSelector, IEnumerable<TValue> values)
{
            if (null == valueSelector) { throw new ArgumentNullException("valueSelector"); }

            if (null == values) { throw new ArgumentNullException("values"); }

            ParameterExpression p = valueSelector.Parameters.Single();

            if (!values.Any())
            {
                return e => false;
            }

            var equals = values.Select(value => (Expression)Expression.Equal(valueSelector.Body, Expression.Constant(value, typeof(TValue))));

            var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.Or(accumulate, equal));

            return Expression.Lambda<Func<TElement, bool>>(body, p);
}

call the method like this :

var u = context.users.Where(BuildContainsExpression<user, Int32>(e => e.Userid, userids)).ToList();

This will solve your problem.