NHibernate Criteria API: Operator Overloading

time to read 14 min | 2630 words

Today I took the time to add a small but extremely nice feature to NHibernate, operator overloading with the criteria API. I used Steve Eichert's solution (thanks, Steve!).

For reference, here is the the code that I added (below are some examples of using it):

#region Operator Overloading

 

public static AbstractCriterion operator &(AbstractCriterion lhs, AbstractCriterion rhs)

{

       return new AndExpression(lhs, rhs);

}

 

public static AbstractCriterion operator |(AbstractCriterion lhs, AbstractCriterion rhs)

{

       return new OrExpression(lhs, rhs);

}

 

public static AbstractCriterion operator !(AbstractCriterion crit)

{

       return new NotExpression(crit);

}

 

/// <summary>

/// See here for details:

/// http://steve.emxsoftware.com/NET/Overloading+the++and++operators

/// </summary>

public static bool operator false(AbstractCriterion criteria)

{

       return false;

}

 

/// <summary>

/// See here for details:

/// http://steve.emxsoftware.com/NET/Overloading+the++and++operators

/// </summary>

public static bool operator true(AbstractCriterion criteria)

{

       return false;

}

 

#endregion

Here is how you would use it:

IList<Customer> orders = session

       .CreateCriteria(typeof(Customer))

       .Add(Expression.Eq("Name", "Ayende") &&

               Expression.Between("Registered", lastYear, DateTime.Today))

       .List<Customer>();

It gets even better when you use the query generator:

IList<Customer> orders = session

       .CreateCriteria(typeof(Customer))

       .Add(Where.Customer.Name.Eq("Ayende") &&

               Where.Customer.Registered.Between(lastYear, DateTime.Today))

       .List<Customer>();

This code makes me happy.

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