Null Handling

With dbExpression, use the helper method dbex.Null (see dbex) instead of null.
dbExpression requires clarity on types - the use of null should be replaced with dbex.Null when it is expected to produce a SQL statement with a server side NULL. This is because to the CLR, null can be just about anything, from any object to any nullable primitive.

For example, the following query will not compile as the right side of the equality can be just about anything, and dbExpression constrains what is accepted to ensure valid SQL statements.

db.SelectOne<Person>()
    .From(dbo.Person)
    .Where(dbo.Person.LastLoginDate == null)
    .Execute();

This would cause a compilation error: CS0034 Operator '==' is ambiguous on operands of type 'PersonEntity.LastLoginDateField' and '<null>'

While you can cast a null as a specific type, it is preferable to use dbex.Null. The following expressions are both valid and produce identical SQL statements:

// it is known that the equality comparison is to a type of 
// DateTime? as we are casting a CLR null to DateTime?
db.SelectOne<Person>()
    .From(dbo.Person)
    .Where(dbo.Person.LastLoginDate == (DateTime?)null)
    .Execute();

// equality comparison to a NullElement provided by dbex.Null,
// which is fully understood by dbExpression
db.SelectOne<Person>()
    .From(dbo.Person)
    .Where(dbo.Person.LastLoginDate == dbex.Null)
    .Execute();