When I first started using NHibernate I didn't know much about design patterns. My early attempts were messy, ugly, and unstable. I finally learned about the
repository pattern and started using it. Things were great, I was able to write cleaner code and was able to abstract away my use of NHiberante. The thing is, NHibernate's
ISession is already an implementation of this pattern, in my opinion. So abstracting an abstraction just adds an extra layer of complexity. That's not to say that you shouldn't use the repository pattern to persist objects, but for basic reads, using the
ISession directly, has a lot of benefits. (For a more thorough analysis see Ayende's blog
here and
here.)
There is, however, one advantage to abstracting away the
ISession. It allows you to unit test your code in a much easier fashion. Since you can easily mock out your repository object, you can write unit tests for modules that use it. This is much easier than if you used the
ISession directly. Whether you use the Criteria, QueryOver, or the Linq Query apis, it's almost impossible to stub out this interaction. If you do happen to stub it out using a mocking framework, your unit test
Arrange step would become so messy, that your unit tests would become completely unreadable.
So what's the solution? In a recent project, we decided not to abstract away, NHibernate when doing queries. Of course, we ran up against the problem of unit testing the code. The solution was remarkable simple. Since we were using the QueryOver api, all we did was write a QueryOverStub implementation of the
IQueryOver<TRoot, TSub>interface. Here's a simple implementation with unused methods not being implemented.
public class QueryOverStub<TRoot, TSub> : IQueryOver<TRoot, TSub>
{
private readonly TRoot _singleOrDefault;
private readonly IList<TRoot> _list;
private readonly ICriteria _root = MockRepository.GenerateStub<ICriteria>();
public QueryOverStub(IList<TRoot> list)
{
_list = list;
}
public QueryOverStub(TRoot singleOrDefault)
{
_singleOrDefault = singleOrDefault;
}
public ICriteria UnderlyingCriteria
{
get { return _root; }
}
public ICriteria RootCriteria
{
get { return _root; }
}
public IList<TRoot> List()
{
return _list;
}
public IList<U> List<U>()
{
throw new NotImplementedException();
}
public IQueryOver<TRoot, TRoot> ToRowCountQuery()
{
throw new NotImplementedException();
}
public IQueryOver<TRoot, TRoot> ToRowCountInt64Query()
{
throw new NotImplementedException();
}
public int RowCount()
{
return _list.Count;
}
public long RowCountInt64()
{
throw new NotImplementedException();
}
public TRoot SingleOrDefault()
{
return _singleOrDefault;
}
public U SingleOrDefault<U>()
{
throw new NotImplementedException();
}
public IEnumerable<TRoot> Future()
{
return _list;
}
public IEnumerable<U> Future<U>()
{
throw new NotImplementedException();
}
public IFutureValue<TRoot> FutureValue()
{
throw new NotImplementedException();
}
public IFutureValue<U> FutureValue<U>()
{
throw new NotImplementedException();
}
public IQueryOver<TRoot, TRoot> Clone()
{
throw new NotImplementedException();
}
public IQueryOver<TRoot> ClearOrders()
{
return this;
}
public IQueryOver<TRoot> Skip(int firstResult)
{
return this;
}
public IQueryOver<TRoot> Take(int maxResults)
{
return this;
}
public IQueryOver<TRoot> Cacheable()
{
return this;
}
public IQueryOver<TRoot> CacheMode(CacheMode cacheMode)
{
return this;
}
public IQueryOver<TRoot> CacheRegion(string cacheRegion)
{
return this;
}
public IQueryOver<TRoot, TSub> And(Expression<Func<TSub, bool>> expression)
{
return this;
}
public IQueryOver<TRoot, TSub> And(Expression<Func<bool>> expression)
{
return this;
}
public IQueryOver<TRoot, TSub> And(ICriterion expression)
{
return this;
}
public IQueryOver<TRoot, TSub> AndNot(Expression<Func<TSub, bool>> expression)
{
return this;
}
public IQueryOver<TRoot, TSub> AndNot(Expression<Func<bool>> expression)
{
return this;
}
public IQueryOverRestrictionBuilder<TRoot, TSub> AndRestrictionOn(Expression<Func<TSub, object>> expression)
{
throw new NotImplementedException();
}
public IQueryOverRestrictionBuilder<TRoot, TSub> AndRestrictionOn(Expression<Func<object>> expression)
{
throw new NotImplementedException();
}
public IQueryOver<TRoot, TSub> Where(Expression<Func<TSub, bool>> expression)
{
return this;
}
public IQueryOver<TRoot, TSub> Where(Expression<Func<bool>> expression)
{
return this;
}
public IQueryOver<TRoot, TSub> Where(ICriterion expression)
{
return this;
}
public IQueryOver<TRoot, TSub> WhereNot(Expression<Func<TSub, bool>> expression)
{
return this;
}
public IQueryOver<TRoot, TSub> WhereNot(Expression<Func<bool>> expression)
{
return this;
}
public IQueryOverRestrictionBuilder<TRoot, TSub> WhereRestrictionOn(Expression<Func<TSub, object>> expression)
{
return new IQueryOverRestrictionBuilder<TRoot, TSub>(this, "prop");
}
public IQueryOverRestrictionBuilder<TRoot, TSub> WhereRestrictionOn(Expression<Func<object>> expression)
{
return new IQueryOverRestrictionBuilder<TRoot, TSub>(this, "prop");
}
public IQueryOver<TRoot, TSub> Select(params Expression<Func<TRoot, object>>[] projections)
{
return this;
}
public IQueryOver<TRoot, TSub> Select(params IProjection[] projections)
{
return this;
}
public IQueryOver<TRoot, TSub> SelectList(Func<QueryOverProjectionBuilder<TRoot>, QueryOverProjectionBuilder<TRoot>> list)
{
return this;
}
public IQueryOverOrderBuilder<TRoot, TSub> OrderBy(Expression<Func<TSub, object>> path)
{
return new IQueryOverOrderBuilder<TRoot, TSub>(this, path);
}
public IQueryOverOrderBuilder<TRoot, TSub> OrderBy(Expression<Func<object>> path)
{
return new IQueryOverOrderBuilder<TRoot, TSub>(this, path, false);
}
public IQueryOverOrderBuilder<TRoot, TSub> OrderBy(IProjection projection)
{
return new IQueryOverOrderBuilder<TRoot, TSub>(this, projection);
}
public IQueryOverOrderBuilder<TRoot, TSub> OrderByAlias(Expression<Func<object>> path)
{
return new IQueryOverOrderBuilder<TRoot, TSub>(this, path, true);
}
public IQueryOverOrderBuilder<TRoot, TSub> ThenBy(Expression<Func<TSub, object>> path)
{
return new IQueryOverOrderBuilder<TRoot, TSub>(this, path);
}
public IQueryOverOrderBuilder<TRoot, TSub> ThenBy(Expression<Func<object>> path)
{
return new IQueryOverOrderBuilder<TRoot, TSub>(this, path, false);
}
public IQueryOverOrderBuilder<TRoot, TSub> ThenBy(IProjection projection)
{
return new IQueryOverOrderBuilder<TRoot, TSub>(this, projection);
}
public IQueryOverOrderBuilder<TRoot, TSub> ThenByAlias(Expression<Func<object>> path)
{
return new IQueryOverOrderBuilder<TRoot, TSub>(this, path, true);
}
public IQueryOver<TRoot, TSub> TransformUsing(IResultTransformer resultTransformer)
{
return this;
}
public IQueryOverFetchBuilder<TRoot, TSub> Fetch(Expression<Func<TRoot, object>> path)
{
return new IQueryOverFetchBuilder<TRoot, TSub>(this, path);
}
public IQueryOverLockBuilder<TRoot, TSub> Lock()
{
throw new NotImplementedException();
}
public IQueryOverLockBuilder<TRoot, TSub> Lock(Expression<Func<object>> alias)
{
throw new NotImplementedException();
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<TSub, U>> path)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<U>> path)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<TSub, U>> path, Expression<Func<U>> alias)
{
return new QueryOverStub<TRoot, U>(_list);
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<U>> path, Expression<Func<U>> alias)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<TSub, U>> path, JoinType joinType)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<U>> path, JoinType joinType)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<TSub, U>> path, Expression<Func<U>> alias, JoinType joinType)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<U>> path, Expression<Func<U>> alias, JoinType joinType)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<TSub, IEnumerable<U>>> path)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<IEnumerable<U>>> path)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<TSub, IEnumerable<U>>> path, Expression<Func<U>> alias)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<IEnumerable<U>>> path, Expression<Func<U>> alias)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<TSub, IEnumerable<U>>> path, JoinType joinType)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<IEnumerable<U>>> path, JoinType joinType)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<TSub, IEnumerable<U>>> path, Expression<Func<U>> alias, JoinType joinType)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, U> JoinQueryOver<U>(Expression<Func<IEnumerable<U>>> path, Expression<Func<U>> alias, JoinType joinType)
{
return new QueryOverStub<TRoot, U>(new List<TRoot>());
}
public IQueryOver<TRoot, TSub> JoinAlias(Expression<Func<TSub, object>> path, Expression<Func<object>> alias)
{
return this;
}
public IQueryOver<TRoot, TSub> JoinAlias(Expression<Func<object>> path, Expression<Func<object>> alias)
{
return this;
}
public IQueryOver<TRoot, TSub> JoinAlias(Expression<Func<TSub, object>> path, Expression<Func<object>> alias, JoinType joinType)
{
return this;
}
public IQueryOver<TRoot, TSub> JoinAlias(Expression<Func<object>> path, Expression<Func<object>> alias, JoinType joinType)
{
return this;
}
public IQueryOverSubqueryBuilder<TRoot, TSub> WithSubquery
{
get { return new IQueryOverSubqueryBuilder<TRoot, TSub>(this); }
}
public IQueryOverJoinBuilder<TRoot, TSub> Inner
{
get { return new IQueryOverJoinBuilder<TRoot, TSub>(this, JoinType.InnerJoin); }
}
public IQueryOverJoinBuilder<TRoot, TSub> Left
{
get { return new IQueryOverJoinBuilder<TRoot, TSub>(this, JoinType.LeftOuterJoin); }
}
public IQueryOverJoinBuilder<TRoot, TSub> Right
{
get { return new IQueryOverJoinBuilder<TRoot, TSub>(this, JoinType.RightOuterJoin); }
}
public IQueryOverJoinBuilder<TRoot, TSub> Full
{
get { return new IQueryOverJoinBuilder<TRoot, TSub>(this, JoinType.FullJoin); }
}
}
So you can easily specify the item or list of items you want the query to return in your test.
new QueryOverStub<Entity, Entity>(new List<Entity>())
The only thing missing is: if you're using projections or getting something like the count. In order to make this implementation work in those situations, we would just need to write implementations for the
List<U> and
SingleOrDefault<U> methods. In an upcoming blog post I'll talk about how to use an in memory Sqlite database as an alternative to using this stub.
