every example I seen shows how to do a update query in linq to sql by doing this.
// grab entity you want to update
entity.UserId = "123"; // update the fields you want to update.
entity.Name = "bob";
Dbcontext.SubmitChanges();
I am wondering can you juse pass in a new object and have it figure it out?
Like could I do this?
Enity myEntity = new Entity();
myEntity.UserId = "123";
myEntity.Name = bob:
// grab entity record
// shove record ito the found record
// it figured out what to update and what no to update
Depending on what exactly you want to do you either need the InsertOnSubmit method, or the Attach method of the respective table (i.e. dbContext.Entities). InsertOnSubmit is used to add a record, while Attach can be used if you want to affect an UPDATE without having to first SELECT the record (you already know the primary key value)
In the case you have the dbContext available and ready, just add InsertOnSubmit:
Entity myEntity = new Entity();
myEntity.UserId = "123";
myEntity.Name = bob:
Dbcontext.InsertOnSubmit(myEntity);
Dbcontext.SubmitChanges();
As the name of the method implies, this will insert your new entity into the database on calling SubmitChanges.
Marc
If you want to do this for performance reasons then you shouldn't worry about it. Linq to Sql will cache objects locally so that just grabbing an entity by ID to modify some fields is very cheap.
It's possible to attach and persist it to the database, however you may want to set a field to check for concurrency (ie LastModified).
If you are going to use the Attach method on the data context, you need to set the primary/composite keys before you attach the entity (so you don't trigger INotifyPropertyChanging, INotifyPropertyChanged events).
Related
Its more than just insert, really. If I already have a partially loaded DAO, how can I load the rest of it?
What I'm going to do is to do a select query, and then use BeanCopy. I'd rather have the result set mapper directly set the properties on the DAO.
Ok, let me try to answer this. For all generated values (like auto-generated IDs) you can use the following flow:
q = DbEntitySql.insert(foo).query();
// ... or any other way to get DbQuery
q.setGeneratedColumns("ID");
q.executeUpdate();
DbOomUtil.populateGeneratedKeys(dao, q);
Basically, for each query/dao you need to specify fields that are autogenerated. Currently there is no annotation for doing so - we are trying to keep number of annotations small as possible. We are working on making this more automatic.
Now, for populating the DAO. I would not use BeanCopy - simply load new DAO instance and ditch the old one. So after you execute the full select query you will get the full DAO loaded, and just continue with it.
I'm a bit confused in regards to how EF's dbContext works.
If I do something like _context.Persons.Add(_person) (assuming person is a valid entity), if I then (before calling _context.SaveChanges()) query Persons, will the person I just added be included in the results?
For example:
Person _person = new Person() {Firstname = "Bill", Lastname = "Snerdly"};
_context.Persons.Add(_person);
var _personList = _context.Persons.Where(p => p.Lastname.StartsWith("Sne"));
Whenever I try this, it seems as though the context loses track of the fact that I've added this new person to the context.
What confuses me is that if I edit an existing person and attach the person and set the state to modified, querying the context seems to keep track of the changes that were made and returns them in the results. For example:
//Assuming that Person 5 exists with the name William Snerdly
Person _person = new Person() {Id = 5, Firstname = "Bill", Lastname = "Snerdly"};
_context.Persons.Attach(_person);
_context.Entry(_person).State = System.Data.EntityState.Modified;
var _personList = _context.Persons.Where(p => p.Lastname.StartsWith("Sne"));
In this case, it seems like the person with the id of 5 will show up in the list with the name Bill instead of William. IOW, the context queried the data but retained the changes while in the first scenario, the context queried the data but ignored any added items. It just seems a bit inconsistant.
Am I understanding this correctly or am I missing something?
Thanks for your help with this.
No, as it does not yet exist in the database. It will, however, be accessible through the ObjectStateManager of the ObjectContext, or alternatively, if you're using the DbContext/DbSet wrappers, through the .Local property of the DbSet.
In the case of the edit, you're seeing the ORM's first level cache at work. The query is executed against the database (and so compares against the values in there - your example would get even weirder if you modified the Lastname in the context, but still get the result from the query looking for the unmodified Lastname), but when its results are processed, first the ID of the returned entity is checked, and since the entity with that ID is already present in the context, you get that instance back. This is the default "AppendOnly" mode of operation.
I don't know what you want to do, but I had to understand all that when I wanted to validate my changes according to rules that needed to use the values of both loaded and unread entities. I ended up starting a transaction, saving the changes with the "None" options, doing my validation queries againt the database (which then contained the "merged" view of the data), and the rolling back the transaction if the data was invalid, or accepting the changes and committing the transaction otherwise.
I'm using yii active records for mysql, and i have a table where there's a field that needs to be appended with the primary key of the same table. The primary key is an auto increment field, hence i can't access the primary key before saving.
$model->append_field = "xyz".$model->id; // nothing is appending
$model->save();
$model->append_field = "xyz".$model->id; //id is now available
How do i do this?
I know that i can update right after insertion, but is there a better method?
Your record is only assigned an id after the INSERT statement is executed. There is no way to determine what that id is prior to INSERT, so you would have to execute an UPDATE with the concatenated field value after your INSERT.
You could write a stored procedure or trigger in MySQL to do this for you, so your app executes a single SQL statement to accomplish this. However, you are just moving the logic into MySQL and in the end both an INSERT and UPDATE are occurring.
Some more workarounds:
This is almost your approach ;)
$model->save();
$model->append_field = "xyz".$model->id; //id is now available
$model->save();
But you could move this functionality to a behavior with a custom afterSave() method, note that you'd have to take care about not looping the event.
Or just write a getter for it
function getFull_append_field(){
return $this->append_field.$this->id;
}
but then you can not use it in a SQL statement, unless you create the attribute there with CONCAT() or something similar.
Anyone else coming to this question might be interested in exactly how i implemented it, so here's the code :
//in the model class
class SomeModel extends CActiveRecord{
...
protected function afterSave(){
parent::afterSave();
if($this->getIsNewRecord()){
$this->append_field=$this->append_field.$this->id;
$this->updateByPk($this->id, array('append_field'=>$this->append_field));
}
}
}
One way to avoid the looping the event(as mentioned by #schmunk) was to use saveAttributes(...) inside the afterSave() method, but saveAttributes(...) checks isNewRecord, and inserts a value only if it is a new record, so that requires us to use setNewRecord(false); before calling saveAttributes(...).
I found that saveAttributes(...) actually calls updateByPk(...) so i directly used updateByPk(...) itself.
In LINQ-to-SQL if I update an object in the context but haven't called SubmitChanges, is there a way to "undo" or abandon that update so that the changes won't get submitted when I eventually call SubmitChanges?
For example, if I've updated several objects and then decide I want to abandon the changes to one of them before submitting.
Part 2: same question for Entity Framework, v3.5
Both LINQ to SQL and Entity Framework will use the same call (assuming you still have the active Context):
_dbContext.Refresh(RefreshMode.OverwriteCurrentValues, yourObj);
A more appropriate way would be to treat the Context as a Unit of Work, in which case you would no longer have an active context when refreshing the object. You would simply dispose of the object you're using currently and get a fresh copy from a new context.
I think you can use the .GetOriginalEntityState(yourEntity) to retrieve the original values. Then set your updated entity back to the original
dim db as new yourDataContext
//get entity
dim e1 as yourEntity = (from x in db.table1).take(1)
//update entity
e1.someProperty = 'New Value'
//get original entity
dim originalEntity = db.table1.getOrignalEntityState(e1)
e1 = originalEntity
db.submitChanges()
Very pseudo-code but I think it conveys the right idea. Using this method, you could also just undo one or more property changes without refreshing the entire entity.
Consider the following code block:
using (PlayersDataContext context = new PlayersDataContext())
{
Console.WriteLine(context.Players.Count()); // will output 'x'
context.Players.InsertOnSubmit(new Player {FirstName = "Vince", LastName = "Young"});
Console.WriteLine(context.Players.Count()); // will also output 'x'; but I'd like to output 'x' + 1
}
Given that I haven't called
context.SubmitChanges();
the application will output the same player count both before and after the InsertOnSubmit statement.
My two questions:
Can the DataContext instance return collections that include pending changes?
Or must I reconcile the DataContext instance with context.GetChangeSet()?
Sure, use:
context.GetChangeSet()
and for more granularity, there are members for Inserts, Updates, and Deletes.
EDIT: I understand your new question now. Yes, if you wanted to include changes in the collection, you would have to somehow combine the collections returned by GetChangeSet() and your existing collections.