Best way to check if object exists in Entity Framework?

If you don't want to execute SQL directly, the best way is to use Any(). This is because Any() will return as soon as it finds a match. Another option is Count(), but this might need to check every row before returning.

Here's an example of how to use it:

if (context.MyEntity.Any(o => o.Id == idToMatch))
{
    // Match!
}

And in vb.net

If context.MyEntity.Any(function(o) o.Id = idToMatch) Then
    ' Match!
End If

I had some trouble with this - my EntityKey consists of three properties (PK with 3 columns) and I didn't want to check each of the columns because that would be ugly. I thought about a solution that works all time with all entities.

Another reason for this is I don't like to catch UpdateExceptions every time.

A little bit of Reflection is needed to get the values of the key properties.

The code is implemented as an extension to simplify the usage as:

context.EntityExists<MyEntityType>(item);

Have a look:

public static bool EntityExists<T>(this ObjectContext context, T entity)
        where T : EntityObject
    {
        object value;
        var entityKeyValues = new List<KeyValuePair<string, object>>();
        var objectSet = context.CreateObjectSet<T>().EntitySet;
        foreach (var member in objectSet.ElementType.KeyMembers)
        {
            var info = entity.GetType().GetProperty(member.Name);
            var tempValue = info.GetValue(entity, null);
            var pair = new KeyValuePair<string, object>(member.Name, tempValue);
            entityKeyValues.Add(pair);
        }
        var key = new EntityKey(objectSet.EntityContainer.Name + "." + objectSet.Name, entityKeyValues);
        if (context.TryGetObjectByKey(key, out value))
        {
            return value != null;
        }
        return false;
    }

Best way to do it

Regardless of what your object is and for what table in the database the only thing you need to have is the primary key in the object.

C# Code

var dbValue = EntityObject.Entry(obj).GetDatabaseValues();
if (dbValue == null)
{
   Don't exist
}

VB.NET Code

Dim dbValue = EntityObject.Entry(obj).GetDatabaseValues()
If dbValue Is Nothing Then
   Don't exist
End If