Linked Entity Query with a mixture of null and not null values returns wrong value

[daveb84]

I have a query that returns columns from a linked entity. When the value of one of the fields of the linked entity is null, it being returned as the value of the previous entity when it should be being returned as null.

e.g.
I have forked the repo and added a unit test - see this commit:
daveb84@b17605d

Full test code:

[Fact]
public void TestRetriveMultipleWithLinkEntityWithAlternateNullField()
{
    // ARRANGE

    List<Entity> initialEntities = new List<Entity>();

    Entity parentEntity = new Entity("parent");
    parentEntity["parentname"] = "parent name";
    parentEntity.Id = Guid.NewGuid();
    initialEntities.Add(parentEntity);

    // create the first child which has the "myvalue" field set to "value"
    Entity childEntity1 = new Entity("child");
    childEntity1["parent"] = parentEntity.ToEntityReference();
    childEntity1["name"] = "entity1";
    childEntity1["myvalue"] = "value";
    childEntity1.Id = Guid.NewGuid();
    initialEntities.Add(childEntity1);

    // create the second child which has the "myvalue" field set to null
    Entity childEntity2 = new Entity("child");
    childEntity2["parent"] = parentEntity.ToEntityReference();
    childEntity2["name"] = "entity2";
    childEntity2["myvalue"] = null;
    childEntity2.Id = Guid.NewGuid();
    initialEntities.Add(childEntity2);

    XrmFakedContext context = new XrmFakedContext();
    IOrganizationService service = context.GetOrganizationService();

    context.Initialize(initialEntities);

    // the query selects the "parent" entity, and joins to the "child" entities
    QueryExpression query = new QueryExpression("parent");
    query.ColumnSet = new ColumnSet("parentname");

    LinkEntity link = new LinkEntity("parent", "child", "parentid", "parent", JoinOperator.Inner);
    link.EntityAlias = "c";
    link.Columns = new ColumnSet("name", "myvalue");

    query.LinkEntities.Add(link);

    // ACT

    DataCollection<Entity> results = service.RetrieveMultiple(query).Entities;

    // ASSERT

    // fields for the first entity work as expected...
    string entity1Name = results[0].GetAttributeValue<AliasedValue>("c.name").Value as string;
    string entity1Value = results[0].GetAttributeValue<AliasedValue>("c.myvalue").Value as string;
        
    Assert.Equal("entity1", entity1Name);
    Assert.Equal("value", entity1Value);

    // fields for the second entity do not.  
    // The child "name" field is correct, but the "myvalue" field is returning the value of the previous
    // entity when it should be returning null
    string entity2Name = results[1].GetAttributeValue<AliasedValue>("c.name").Value as string;
    string entity2Value = results[1].GetAttributeValue<AliasedValue>("c.myvalue").Value as string;

    // this works fine:
    Assert.Equal("entity2", entity2Name);

    // this fails (entity2Value is "value")
    Assert.Equal(null, entity2Value);
}

[JanFelixReuter]

We have stumbled upon the same issue. Here is another test to reproduce it:

[TestMethod]
public void Attributes_Dont_Bleed_Into_Other_Records_When_Joining()
{
    var organizationService = new FakeXrmEasy.XrmFakedContext().GetOrganizationService();

    var mainId = organizationService.Create(new Entity("main"));

    //NOTE: The order of creation of the linked entities is important.
    //Linked entity with attribute set to a value
    organizationService.Create(new Entity("linked")
    {
        Attributes = new AttributeCollection {{"mainid", mainId}, {"attribute", "Data"}}
    });

    //Linked entity with attribute set to null
    organizationService.Create(new Entity("linked")
    {
        Attributes = new AttributeCollection {{"mainid", mainId}, {"attribute", null}}
    });

    //Linked entity with attribute not set at all
    organizationService.Create(new Entity("linked")
    {
        Attributes = new AttributeCollection { { "mainid", mainId } }
    });

    var queryExpression = new QueryExpression("main")
    {
        ColumnSet = new ColumnSet(true),
        LinkEntities =
        {
            new LinkEntity("main", "linked", "mainid", "mainid", JoinOperator.Inner)
            {
                EntityAlias = "linked",
                Columns = new ColumnSet(true)
            }
        }
    };

    //Should return all three linked records
    var result = organizationService.RetrieveMultiple(queryExpression);

    //Get attribute values of all linked entities
    var attributeValues = result.Entities
            .Select(e => e.Attributes.TryGetValue("linked.attribute", out var value) ? (value as AliasedValue)?.Value : null)
            .ToList(); 

    //Should get 1x Data and 2x null
    attributeValues.Should().BeEquivalentTo(new object[] {"Data", null, null});
    //Actual values: "Data", "Data", "Data"
}

The problem appears to be in the method JoinAttributes. The "main" e entity gets re-used for every linked entity. Attributes from previous linked entities are not overwritten when they are null.