NHibernate

Session.Merge(object obj) to RESCUE

January 29, 2010 Errors, NHibernate No comments

Error:

“a different object with the same identifier value was already associated with the session: 14, of entity: Developer.RoadMap.To.Success.Entities.Customer”

I had something like this in the SaveCustomer method:

if ( customer.CustomerID > 0 )
{
    Session.Update( customer);
}
else
{
    Session.SaveOrUpdate( customer);
}
transaction.Commit();

And this don’t work correctly. Simple change to

if ( customer.CustomerID > 0 )
{
    customer = Session.Merge( customer );
}
else
{
    Session.SaveOrUpdate( customer);
}
transaction.Commit();

resolved my issue.


No comments

Quick Verification if row exists in database with Nhibernate

December 23, 2009 NHibernate No comments

Next SQL, which verifies if customer row exists in database:

SELECT customer0_.CUSTOMER_ID AS x0_0_
FROM   T_CUSTOMER customer0_
WHERE  (customer0_.CUSTOMER_ID = 123456)

Will be generated with next NHibernate Query:

public bool CustomerExistsInDatabase(Int32 customerId)
{
    var result = Session.CreateQuery(string.Format(“select c.CustomerID from Customer c where c.CustomerID = {0}”, customerId)).UniqueResult<Int32?>();

    return result.HasValue;
}

Please note, that you could use not only primary key, but any other property in your where condition.


No comments

NHibernate: The column name COLUMN_ID is specified more than once in the SET clause

December 9, 2009 NHibernate 4 comments

Sometime ago I faced with NHibernate issue and spent much time on figuring out how to resolve it. Issue was with saving complicated entity.
Error:

The column name ‘RESOURCE_ID’ is specified more than once in the SET clause. A column cannot be assigned more than one value in the same SET clause. Modify the SET clause to make sure that a column is updated only once. If the SET clause updates columns of a view, then the column name ‘RESOURCE_ID’ may appear twice in the view definition.

With NHibernate Profiler I found that this fails on the next SQL: 

UPDATE SOME_TABLE SET SOME_COLUMN1 = ?, SOME_COLUMN2 = ?, RESOURCE_ID = ?, SOMETHING_ELSE = ?, RESOURCE_ID = ? WHERE SOME_TABLE_ID = ?

With better look you will see that there two times RESOURCE_ID mentioned so this looks like wrong mapping. But I was sure that everything is ok there.

This two References are wrong.
At first glance do you see why? At that moment I was not able also.

References(x => x.Resource)
        .Access.AsCamelCaseField(Prefix.Underscore)
        .WithForeignKey(“RESOURCE_ID”).TheColumnNameIs(“RESOURCE_ID”)
        .FetchType.Join();

References(x => x.ResourceRole)
        .Access.AsCamelCaseField(Prefix.Underscore)
        .WithColumns(“RESOURCE_ROLE_ID”, “RESOURCE_ID”)
        .FetchType.Join();

Here Resource has key (RESOURCE_ID).
ResourceRole has composite key (ROLE_ID and RESOURCE_ID).

After long searching and many tries I found why mapping is not correct. Even have my explanation for it.

When we reference ResourceRole we already use RESOURCE_ID field, so when we setup Resource and say “Hey, there is one more RESOURCE_ID“, then NHibernate cannot find out how to update all this correctly.

Solution:
insert=”false” update=”false” attributes for one of references solves the issue.

In Fluent NHibernate it looks like:

.SetAttribute(“update”, “false”);


4 comments

NHibernate Criteria for Nullable property

December 7, 2009 NHibernate 2 comments

Image that you want to fetch friends from database by the First Name, Last Name and Age, which are properties of your class Friend. With NHibernate you could write query which will look like:

public IList<Friend> GetFriends(string firstName, string lastName, int? age)
{
    IList<Friend> friends = Session.CreateCriteria(typeof(Friend))
        .Add(Expression.Eq(“FirstName”, firstName))
        .Add(Expression.Eq(“LastName”, lastName))
        .Add(Expression.Eq(“Age”, age))
        .List<Friend>();

    return friends;
}

But it is wrong. Since Age is the Nullable type (int?), your call GetFriends(“Andriy”,”Buday”,null) will not get my record even if there is such in database and the column AGE is NULL there. So to request you need this: ageExpression = Expression.IsNull(“Age”); but it will not work for not null age.
For our luck there is AbstractCriterion so we can generalize our Expressions like here:

public IList<Friend> GetFriends(string firstName, string lastName, int? age)
{
    AbstractCriterion ageExpression;
    if (age == null)
    {
        ageExpression = Expression.IsNull(“Age”);
    }
    else
    {
        ageExpression = Expression.Eq(“Age”, age);
    }

    IList<Friend> friends = Session.CreateCriteria(typeof(Friend))
        .Add(Expression.Eq(“FirstName”, firstName))
        .Add(Expression.Eq(“LastName”, lastName))
        .Add(ageExpression)
        .List<Friend>();

    return friends;
}


2 comments