LINQ to Entities how to update a record

Question

Okay, so I'm new to both EF and LINQ. I have figured out how to INSERT and DELETE but for some reason UPDATE seems to escape my grasp.

Here is a sample of my code:

EntityDB dataBase = new EntityDB();
Customer c = new Customer
{
     Name = "Test",
     Gender = "Male
};
dataBase.Customers.AddObject(c);
dataBase.SaveChanges();

The above creates and adds a record just fine.

Customer c = (from x in dataBase.Customers
             where x.Name == "Test"
             selext x).First();
dataBase.Customers.DeleteObject(c);
dataBase.SaveChanges();

The above effectively deletes the specified record.

Now how do I update? I can't seem to find an "UpdateObject()" method on the entity collection.

If you are using EF4, I'd prefer this solution http://stackoverflow.com/questions/623672/update-entity-framework-objects — D.Rosado, Dec 07 '12 at 10:38

score 84 · Accepted Answer · edited Aug 27 '15 at 10:20

84

Just modify one of the returned entities:

Customer c = (from x in dataBase.Customers
             where x.Name == "Test"
             select x).First();
c.Name = "New Name";
dataBase.SaveChanges();

Note, you can only update an entity (something that extends EntityObject, not something that you have projected using something like select new CustomObject{Name = x.Name}

edited Aug 27 '15 at 10:20

erictrigo

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answered Jan 06 '11 at 17:36

tster

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I did that. For some reason it is not persisting the changes to the database. – CatDadCode Jan 06 '11 at 17:37
@Chevex: But note that it get a lot more involved when using another context instance. – H H Jan 06 '11 at 17:47
What does it mean to "use another context instance"? – CatDadCode Jan 06 '11 at 17:52
I've tried it, but for some reason, in my case it duplicates instead of update. The old record is maintained and a new record is created with the information of the record I suppose to update. What is happening? – cgalvao1993 Dec 03 '13 at 17:39

score 8 · Answer 2 · edited Feb 26 '18 at 12:54

8

//for update

(from x in dataBase.Customers
         where x.Name == "Test"
         select x).ToList().ForEach(xx => xx.Name="New Name");

//for delete

dataBase.Customers.RemoveAll(x=>x.Name=="Name");

edited Feb 26 '18 at 12:54

Mamun

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answered Apr 10 '14 at 12:55

Zohaib Iqbal

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score 3 · Answer 3 · answered Jan 06 '11 at 17:38

3

They both track your changes to the collection, just call the SaveChanges() method that should update the DB.

answered Jan 06 '11 at 17:38

Anthony

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score 0 · Answer 4 · answered Jan 02 '20 at 16:22

In most cases @tster's answer will suffice. However, I had a scenario where I wanted to update a row without first retrieving it.

My situation is this: I've got a table where I want to "lock" a row so that only a single user at a time will be able to edit it in my app. I'm achieving this by saying

update items set status = 'in use', lastuser = @lastuser, lastupdate = @updatetime where ID = @rowtolock and @status = 'free'

The reason being, if I were to simply retrieve the row by ID, change the properties and then save, I could end up with two people accessing the same row simultaneously. This way, I simply send and update claiming this row as mine, then I try to retrieve the row which has the same properties I just updated with. If that row exists, great. If, for some reason it doesn't (someone else's "lock" command got there first), I simply return FALSE from my method.

I do this by using context.Database.ExecuteSqlCommand which accepts a string command and an array of parameters.

Just wanted to add this answer to point out that there will be scenarios in which retrieving a row, updating it, and saving it back to the DB won't suffice and that there are ways of running a straight update statement when necessary.

LINQ to Entities how to update a record

4 Answers4

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