Entity framework query on just added but not saved values

Question

I'm using Entity Framework from a couple of years and I have a little problem now.

I add an entity to my table, with

Entities.dbContext.MyTable.Add(obj1);

and here ok.

Then, I'd like to make a query on MyTable, like

Entities.dbContext.MyTable.Where(.....)

The code above will query on my MyTable in the db.

Is there a way to query also on the just added value, before the saveChanges? (obj1) How?

UPDATE

Why do I need this? Because, for each new element I add, I need to edit some values in the previous and the next record (there is a datetime field in this table)

UPDATE2

Let's say I have to add a lot of objects, but I call the saveChanges only after the last item is added. Every time I add the new item, I read its datetime field and I search in the database the previous and the next record. Here, I edit a field of the previous and of the next record. Now, here is problem: if I insert another item, and, for example, the next item is "Obj1", I have to find and edit it, but I can't find it since I haven't saved my changes. Is it clearer now?

Why would you want to? You have the object already, it's stored as `obj1` — Alfie Goodacre, Dec 06 '16 at 15:48
As soon as you call SaveChanges obj1 will contain anything just saved, such as it's primary key - no need to re-fetch it. — Darren Wainwright, Dec 06 '16 at 15:50
@PieroAlberto I'm still confused, you have the object so you can still use it to edit other values — Alfie Goodacre, Dec 06 '16 at 15:53
@Darren Not necessarily if there are triggers on the database for creationDate or other calculations the object would have to be reloaded in order to get those values. — Jared Stroebele, Dec 06 '16 at 15:53
@JaredStroeb - perhaps, though he updated the Q after I made my comment. He needs to put far more information in the Q. — Darren Wainwright, Dec 06 '16 at 15:56
Yeah still not clear on what the goal is. Why can you not get your IQueriable collection from the db add the obj1 to the collection then use the collection to find and manipulate the correct entities? — Jared Stroebele, Dec 06 '16 at 15:59
_"I edit a field of the previous and of the next record"_ - how do you define "previous" and "next" - by Id, by Date, by table order or…? — stuartd, Dec 06 '16 at 16:09
@PieroAlberto in which case you can query for those records, amend them accordingly, and then save all three..? — stuartd, Dec 06 '16 at 17:22
@stuartd often. When users add some manually data in a auto-populated table, I have to edit the next and previous one, according to a datetime field, to keep the correct order — Piero Alberto, Dec 07 '16 at 07:11
Is that something that could be done by a database insert trigger? — stuartd, Dec 07 '16 at 10:11

score 23 · Accepted Answer · edited Jul 06 '20 at 20:42

23

You should be able to get your added entities out of the dbContext via the change tracker like this:

 var addedEntities = dbContext.ChangeTracker.Entries()
   .Where(x => x.State == EntityState.Added && x.Entity is Mytable)
   .Select(x => x.Entity as MyTable)
   .Where(t => --criteria--);

Or using the type testing with pattern matching in c# 7.0:

var addedEntities = dbContext.ChangeTracker.Entries()
   .Where(x => x.State == EntityState.Added && x.Entity is Mytable t && --test t for criteria--)
   .Select(x => x.Entity as MyTable);

because you are only querying added entities, you can combine this with

dbContext.MyTable.Where(t => --criteria--).ToList().AddRange(addedEntities);

to get all of the relevant objects

edited Jul 06 '20 at 20:42

palindrom

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answered Dec 06 '16 at 16:13

ste-fu

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1

This is good solution. However it did not work for me, as is. In my case the Entity.GetType().Name was appended with a GUID. So I consider the BaseType as well. Where(x => x.State == EntityState.Added && (x.Entity.GetType() == typeof(MyTable) || x.Entity.GetType().BaseType == typeof(MyTable))) – RitchieD Dec 22 '16 at 14:25
Can you give an hint here about the "addedEntities"? http://stackoverflow.com/questions/41982691/one-databse-two-applications-two-dbconterxt – Piero Alberto Feb 01 '17 at 15:42
Is there any way you can accomplish this without using ChangeTracker? – onhax Oct 11 '18 at 03:12
@onhax I don't think there's an easy method. `ChangeTracker` is what EF uses internally I believe – ste-fu Oct 12 '18 at 08:29
The `Local` property of `DbSet` described in https://stackoverflow.com/a/8468456/548020 might be a more convenient alternative – CodeZombie Aug 14 '19 at 14:50

Jared Stroebele · Answer 2 · 2016-12-06T16:43:43.833

I think this is a good situation for Transactions. I am going to assume you are using EF 6 since you did not provide a version. =)

UPDATE2 changes

public void BulkInsertObj(List<TEntity> objList)
{
    using (var context = new dbContext()) 
    { 
        using (var dbContextTransaction = context.Database.BeginTransaction()) 
        {  
            try 
            { 
                foreach(var obj1 in objList)
                {
                    dbContext.MyTable.Add(obj1);

                    //obj1 should be on the context now 
                    var previousEntity = dbContext.MyTable.Where(.....) //However you determine this
                    previousEntity.field = something

                    var nextEntity = dbContext.MyTable.Where(.....) //However you determine this
                    nextEntity.field = somethingElse
                }

                context.SaveChanges(); 
                dbContextTransaction.Commit(); 
            } 
            catch (Exception) 
            { 
                dbContextTransaction.Rollback(); 
            } 
        } 
    } 
}

MSDN EF6 Transactions

Entity framework query on just added but not saved values

2 Answers2