[Issue #1780] Bug: IncludeGraph fails when first entity has null navigation property

[Lion-Ch]

Fixed the case of inserting child entities, when there could be an entity with an empty child entity at the beginning of the array. Because of this, the subsequent insertion of bundles of entities was performed incorrectly. GroupBy by EntityType in ExecuteWithGraphAsync put the type of entity that was the parent in the first place.

Example

The main entity is Parent - P, the child entity is Child - C.
If there was an array Parent[]

[
new () { Child = null },
new () { Child = new() },
new () { Child = new() },
// ...
]

After sorting, we get: PCPCP

After grouping, we will insert in bundles: Parent[], Child[]. Which is wrong!

If all the Parents had Child, then after sorting we get: CPCPCP
After grouping, we will insert in bundles: Child[], Parent[]. That's right.

Solution

To avoid this problem, an additional sorting by graph depth was added.
For each entity, its depth (length to the vertex) is determined. The maximum depth is determined for each type of entity in order to understand which entities need to be inserted first (the type of entity with the maximum depth) and which last (the type of entity with the minimum depth).

1. For example, after sorting, we get: PCPCP
2. After determining the depth: P(0)C(1)P(0)C(1)P(0)
3. After determining the maximum depth for the type of entity: P = 0, C = 1
4. After applying depth sorting, we get: C(1)C(1)P(0)P(0)P(0)

Further, with GroupBy, the groups will be formed correctly and the identifiers for external entities will be entered correctly.

In summary

• Added additional sorting of the graph by depth
• Added a test to check the insertion of entities (BulkInsertOrUpdate_EntityWithNestedNullableObjectGraph_SavesGraphToDatabase1)
• To activate the old logic, disable withAdditionalSorting in GraphUtil

It remains to be done

• Roll back the database schema and write a new test
• Consider the cases I haven’t accounted for, because this error is the only one I have fixed.
• Add tests for more complex entity graphs and test the algorithm.
• Test performance on large amounts of inserted data (reflection, algorithmic complexity)