c# 4.0 - entity framework: conditional filter

Question

Let's say I have Customers table and I want to filter it by the following:

• Country: All, US, UK, Canada
• Income: All, low, high, medium
• Age:All, teenager, adult, senior

if I had to build an SQL string for this filter, it would be something like this:

if (Country != "All") sql += "country = " + Country
if (Income != "All") sql += "and income = " + Income
if (Age != "All") sql += "and age = " + Age;

So, basically, the user can filter by some, but not necessary all fields.

How do you do this using Entity Framework ?

Thanks !

Answer 1

LINQ to Entity queries return IQueryable's, so you can build your query this way:

IQueryable<Person> query = context.People;

if (Country != "All")
{
    query = query.Where(p => p.Country == Country);
}

if (Income != "All")
{
    query = query.Where(p => p.Income == Income);
}

if (Age != "All")
{
    query = query.Where(p => p.Age == Age);
}

List<Person> fetchedPeople = query.ToList();

This case is almost too simple, but this is very helpful in more complex situations when you need to add filtering dynamically.