Question

Using Entity Framework 4.3 in one of my data access classes I have generic a function like this

    public List<Company> Query(Func<Company, bool> expression)
    {
        return MyDbContext.Instance().Company.Where(expression).ToList();
    }

I use it from the bussines layer classes as MyDAL.Query(a => a.Name.Contains(textToSearch)).

Despite ofEntity Framework return the correct results, I don’t know why it instead of generate a Sql query sentence with Where clause like “Where name like ‘%’ + textToSearch + ‘%'”, It generates a sql query sentence without a where clause query all the table rows. Obviously this is very inneficient.

By the other way if in my data access clases I write a method like this:

    public List<Company> GetLikeName(string textToSearch)
    {
        return MyDbContext.Instance().Company.Where(a => a.Contains(textToSearch)).ToList();
    }

It generates correctly a Sql with where like clause.

Why If I use my generic query to retrieve results from database especifying the expression to query from my bussiness classes it generates a Sql sentence without where clause?

Thanks

Answer 1

You need to pass the expression parameter as an Expression<>:

public List<Company> Query(Expression<Func<Company, bool>> expression)

If you just pass a Func<>, then IEnumerable.Where is called instead of IQueryable.Where, and it runs in code, not in SQL.