EF 6 保存多个级别的子实体和多个父实体

Question

Given this model:

I would like to be able to save in one SaveChange call the relations. Which means, I either have a new or updated ContainerParent, and multiple first level children and each of those can have 1 or 2 levels deeper.

The thing is, the children both have a key to themselves, for finding its parent, and a key to the container, for the container to get all its Children independently of their hierarchical level.

With this pseudo code (in the case of all entities are created, not updated)

var newContainerParent = context.ContainerParents.Add(new ContainerParent());
var rootChild = context.Children.Add(new Child());

var secondLevelChild = new Child();
var thirdLevelChild = new Child();
secondLevelChild.Children.Add(thirdLevelChild);

rootChild.Children.Add(secondLevelChild);
newContainerParent.Children.Add(rootChild);

context.SaveChanges();

Problem with this code, is that only the rootchild will have the FK for the container set. I also tried to add the children to they child parent AND the container:

rootChild.Children.Add(secondLevelChild);
newContainerParent.Children.Add(rootChild);
newContainerParent.Children.Add(secondLevelChild);
newContainerParent.Children.Add(thirdLevelChild);

I have the same problem while updating an existing container with new children. I set all the children with the already existing key of the parent, but when SaveChanges is called the key is not saved, its reverted to null.

I fixed it by doing all this in 2 steps, saving once and then getting all the newly created children and updating them with the parent key, the calling SaveChanges again.

I have a feeling I'm missing something, that I should not need to save twice.

Answer 1

The number or frequence of SaveChange calls have no implication on anything, not on performance or so. So why do you want to minimize it ?

Actually, storing such a self referencing table with one SaveChanges is not possible, cause the ID of an new entity, is generated, when it is saved. So you first need to save it, and then you get the ID, that you can store in another entity. This might require further update-Commands, to the entity you just stored.

You have two chances to solve this.

1) manually generated ID's, handle it all yourself and you know the ID before your store it.

2) In case you have no circularity in your dependency, so a perfect tree structure, you save the items top-down, level by level. I assume you have the childs having a reference to it's parents, so the root has no reference to any other items, you save that first, than the 1st level children, and so on.

This requires multiple SaveChanges, but this is not a disadvantage. It is one Insert-SQL-Command per entity anyway, no matter if you do it in 1 SaveChanges or in 100 SaveChanges.

Both solutions avoid "Update" Commands to the entities, they do Inserts only.

Entity Framework could actually find out this dependencies itself and create an order for new entities to insert, but this is not implemented today, or not perfect, especially on self-referenced tables. The order of saving items is kind of random. So you have to enforce the order with intermediate SaveChanges.