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Thursday, February 15, 2018

DataObjects.Net 5.0.17 Beta 3

We have released a new version of DataObjects.Net

In the version following changes were performed:

[main] Fixed certain scenarios when In() or Contains() operations in query led to  NullReferenceExecption exception
[main] Persist operation no longer breaks enumeration of EntitySet items.

Detailed explanation of these changes is in the post.

As usual you can get it from our website or install from Nuget library.


NullReferenceException during query translation

Sometimes inclusion of a static fields in operations like In() or Contains() resulted in the exception. Instance fields are handled correctly though. For example,

   [TestFixture]
  public class ContainsTest
  {
    // ...
    // some other members 
    // ...

    private static int StaticItemId = 1;
    private int InstanceItemId = 1;

    [Test]
    public void MainTest()
    {
      using (var domain = Domain.Build(GetDomainConfiguration())
      using (var session = domain.OpenSession())
      using (var trasnaction = session.OpenTransaction()) {
        var ids = new[] {1, 2};
        // works fine
        var count = session.Query.All<TestEntity>()
          .Count(e => ids.Contains(InstanceItemId)));

        // used to be a problem
        var count = session.Query.All<TestEntity>()
          .Count(e => ids.Contains(StaticItemId)));
      }
    }
  }

Now both cases work fine.

Persist operation terminates EntitySet items enumeration 

Saving local changes to storage while EntitySet<T> collection is being enumerated caused an exception due to the modification of collection. For instance,

  using (var domain = Domain.Build(GetDomainConfiguration())
  using (var session = domain.OpenSession())
  using (var transaction = session.OpenTransaction()) {
    //get order with some items
    var order = session.Query.All<Order>().First();
    // locally added item
    order.Items.Add(new OrderItem());

    foreach (var orderItems in order.Items) {
      // there are no changes to the collection performed
      // forces local changes to be saved to storage explicitly
      session.SaveChanges();
    }
  }

And an example of implicit saving of changes

  using (var domain = Domain.Build(GetDomainConfiguration())
  using (var session = domain.OpenSession())
  using (var transaction = session.OpenTransaction()) {
    //get order with some items
    var order = session.Query.All<Order>().First();
    // locally added item
    order.Items.Add(new OrderItem());

    foreach (var orderItems in order.Items) {
      // there are no changes to the collection performed
      // implicit saving
      var orderItemCount = session.Query.All<OrderItem>().Count();
    }
  }

Basically, an EntitySet<T> collection consists of three sets - the first set of items is saved to the database, the second set consists of locally added items and the third one is locally removed items. Two last sets store changes of collection between savings them to the storage. A persist operation (saving changes) merges all the three sets into the first one, which caused an exception during enumeration.

This merge mechanism was changed. Now only user changes can be the cause of enumeration termination. If a user adds or removes something from the EntitySet instance which is being currently enumerated it will break the enumeration. See example below:

  using (var domain = Domain.Build(GetDomainConfiguration())
  using (var session = domain.OpenSession())
  using (var transaction = session.OpenTransaction()) {
    //get order with some items
    var order = session.Query.All<Order>().First();
    // locally added item
    order.Items.Add(new OrderItem());

    foreach (var orderItems in order.Items) {
      //we change contents of the EntitySet
      order.Items.Add(new OrderItem());
    }
  }

Here, the EntitySet<Order> collection was modified during enumeration so it should be terminated.

Another case when user implicitly changes EntitySet is a paired association. For instance, for the model showed below

  [HierarchyRoot]
  public class Order : Entity
  {
    [Field, Key]
    public long Id { get; private set; }

    [Field]
    public EntitySet<OrderItem> Items { get; private set; }

    // some other fields

    public Order(Session session) 
      : base(session)
    {}
  }

  [HierarchyRoot]
  public class OrderItem : Entity
  {
    [Field, Key]
    public long Id { get; private set; }

    [Field]
    [Association(PairTo = "Items")]
    public Order Order { get; set; }

    //some other fields

    public OrderItem(Session session)
      : base(session)
    {}
  }

Order.Items and OrderItem.Order fields will remain in synchronized state. That cause modification of Items collection and if such thing happens during the collection enumeration an exception will show up. The code below is a great illustration.

  using (var domain = Domain.Build(GetDomainConfiguration())  
  using (var session = Domain.OpenSession())
  using (var transaction = session.OpenTransaction()) {
    var order = session.Query.All<Order>().First();
    var newOrder = new Order();

    foreach (var orderItem in order.Items) {
      // remove the orderItem from the Items collection
      orderItem.Order = newOrder; 
    }
  }

On the first iteration orderItem entity becomes removed from order.Items collection and added to  newOrder.Items collection by setting orderItem.Order field. On the second iteration enumerator will detect the order.Items collection is changed and throw an exception.

So now EntitySet enumeration works as it is supposed to and causes no exception unless the collection has been changed by user.

















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