I've been banging my head off what should be a simple issue. I'm trying to do the following basic operation
1) Check if entity exists by a field other than ID
2) If not, create entity
Problem is this is in a console app that is multi-threaded, so I need to somehow get an entity by a field other than the ID and set the LockMode to Upgrade (or at least I think thats what needs to be done). From what I see there is no way to do that with ISession.
Any ideas?
in a single process use a global lockobject
lock(existsLocker)
{
var entity = session.Query<Entity>().Where(...).FirstOrDefault();
if (entity == null)
{
entity = new Entity();
session.Save(entity);
session.Flush();
}
}
Related
I'm working on a post method that should have a really good performance.
I have a value in the request body that will look in the database for the row that is connected with that value and return it and add it as a foreign key.
So how it is now:
Look in the database and check if the data already exists
If no add it to the database
Look that added or already existing data in the database and join it to the entity
So now there are 3 calls to the database
I was wondering if there is some kind of GetOrAdd method that will connect the table to my data if it exists and if it not exists add it to the database so it will most of the time only have 1 call to the database instead of always 3 calls
Please read the following doc
Here is an "Insert or Update" pattern:
public void InsertOrUpdate(Blog blog)
{
using (var context = new BloggingContext())
{
context.Entry(blog).State = blog.BlogId == 0 ?
EntityState.Added :
EntityState.Modified;
context.SaveChanges();
}
}
Of note, once you hit SaveChanges() you can expect your in memory object (blog, in this case) to be the same object that is stored in the database, and would not have to make a 3rd call to retrieve it again. EF Core will update the Primary Key with the actual persisted Id.
using (var context = new BloggingContext())
{
var blog = new Blog {Id = 1, Url = "blablabla" };
context.Blogs.Update(blog);
await context.SaveChangesAsync();
}
If a reachable entity has its primary key value set then it will be tracked in the Microsoft.EntityFrameworkCore.EntityState.Modified state. If the primary key value is not set then it will be tracked in the Microsoft.EntityFrameworkCore.EntityState.Add state.
This comment is from Entity Framework Core's Update method. You just need to call Update method if entity is exist in Database it will be updated otherwise will be created as new record.
I am trying to update an object after retrieving it from a database.
This fires 2 queries , one for the select and the other for the update, is there any way of update an object using Fluent NHiberNate firing only one query ?
My code is as below:
var userProfile = userProfileRepository
.Find(x => x.ClientId == clientId)
.FirstOrDefault();
/* update UserProfile object here */
userProfileRepository.SaveOrUpdate(userProfile);
the SaveOrUpdate Method looks as such :
public bool SaveOrUpdate(T instance)
{
using (var session = SessionManager.OpenSession())
{
using (var transaction = session.BeginTransaction())
{
session.SaveOrUpdate(instance);
transaction.Commit();
}
return true;
}
}
In case that your issue is:
regardless of what I do, SaveOrUpdate() always sends SELECT then UPDATE
You should check the doc:
5.1.4.7. Assigned Identifiers
If you want the application to assign identifiers (as opposed to having NHibernate generate them), you may use the assigned generator. This special generator will use the identifier value already assigned to the object's identifier property. Be very careful when using this feature to assign keys with business meaning (almost always a terrible design decision).
Due to its inherent nature, entities that use this generator cannot be saved via the ISession's SaveOrUpdate() method. Instead you have to explicitly specify to NHibernate if the object should be saved or updated by calling either the Save() or Update() method of the ISession.
So, if your Fluent configuration sets the ID to be assigned - NHibernate has no other way then check if it
exists
or is new
because used method was SaveOrUpdate()
Solution(s)
1) Change the ID to be generated by DB or NHiberante 2) use explicit Update()
Are you trying to create an
UPDATE ... WHERE ...
statement?
AFAIK the NHibernate way to do this, is to select the appropriate objects (using the WHERE clause), update the fields, and persist them again.
var tempObjects = _session.Query<myObject>.Where(o => o.Id > 500);
// update proxy objects
foreach (var o in tempObjects)
{
o.MyValue = updatedValue;
}
// commit updated objects
_session.Update(tempObjects);
To be honest, we've used ISession.CreateSQLQuery ourselves. I hate using SQL in code because it breaks in refactoring, but if you must - here's how:
_session.CreateSQLQuery(
#"UPDATE [MyTable] SET [MyValue]=:updatedvalue WHERE Id > 500")
.SetParameter("updatedvalue", updatedValue)
.ExecuteUpdate();
I used Entity Framework to create a prototype for a project and now that it's working I want to make the program ready for production.
I face many challenges with EF, the biggest one being the concurrency management (it's a financial software).
Given that it seems to have no way to handle pessimistic concurrency with EF, I have to switch to stored procs in SQL.
To be honest I'm a bit afraid of the workload that may represent.
I would like to know if anybody have been in the same situation before and what is the best strategy to convert a .net code using EF to raw SQL.
Edit:
I'm investigating CLR but it's not clear if pessimistic concurency can be manage with it. is it an option more interesting than TSQl in this case ? It would allow me to reuse part of my C# code and structure of function calling another functions, if I understand well.
I was there and the good news is you don't have to give up Entity Framework if you don't want to. The bad news is you have to update the database yourself. Which isn't as hard as it seems. I'm currently using EF 5 but plan to go to EF 6. I don't see why this still wouldn't work for EF 6.
First thing is in the constructor of the DbContext cast it to IObjectContextAdapter and get access to the ObjectContext. I make a property for this
public virtual ObjectContext ObjContext
{
get
{
return ((IObjectContextAdapter)this).ObjectContext;
}
}
Once you have that subscribe to the SavingChanges event - this isn't our exact code some things are copied out of other methods and redone. This just gives you an idea of what you need to do.
ObjContext.SavingChanges += SaveData;
private void SaveData(object sender, EventArgs e)
{
var context = sender as ObjectContext;
if (context != null)
{
context.DetectChanges();
var tsql = new StringBuilder();
var dbParams = new List<KeyValuePair<string, object>>();
var deletedEntites = context.ObjectStateManager.GetObjectStateEntries(EntityState.Deleted);
foreach (var delete in deletedEntites)
{
// Set state to unchanged - so entity framework will ignore
delete.ChangeState(EntityState.Unchanged);
// Method to generate tsql for deleting entities
DeleteData(delete, tsql, dbParams);
}
var addedEntites = context.ObjectStateManager.GetObjectStateEntries(EntityState.Added);
foreach (var add in addedEntites)
{
// Set state to unchanged - so entity framework will ignore
add.ChangeState(EntityState.Unchanged);
// Method to generate tsql for added entities
AddData(add, tsql, dbParams);
}
var editedEntites = context.ObjectStateManager.GetObjectStateEntries(EntityState.Modified);
foreach (var edit in editedEntites)
{
// Method to generate tsql for updating entities
UpdateEditData(edit, tsql, dbParams);
// Set state to unchanged - so entity framework will ignore
edit.ChangeState(EntityState.Unchanged);
}
if (!tsql.ToString().IsEmpty())
{
var dbcommand = Database.Connection.CreateCommand();
dbcommand.CommandText = tsql.ToString();
foreach (var dbParameter in dbParams)
{
var dbparam = dbcommand.CreateParameter();
dbparam.ParameterName = dbParameter.Key;
dbparam.Value = dbParameter.Value;
dbcommand.Parameters.Add(dbparam);
}
var results = dbcommand.ExecuteNonQuery();
}
}
}
Why we set the entity to unmodified after the update because you can do
var changed properties = edit.GetModifiedProperties();
to get a list of all the changed properties. Since all the entities are now marked as unchanged EF will not send any updates to SQL.
You will also need to mess with the metadata to go from entity to table and property to fields. This isn't that hard to do but messing the metadata does take some time to learn. Something I still struggle with sometimes. I refactored all that out into an IMetaDataHelper interface where I pass it in the entity type and property name to get the table and field back - along with caching the result so I don't have to query metadata all the time.
At the end the tsql is a batch that has all the T-SQL how we want it with the locking hints and containing the transaction level. We also change numeric fields from just being set to nfield = 10 but to be nfield = nfield + 2 in the TSQL if the user updated them by 2 to avoid the concurrency issue as well.
What you wont get to is having SQL locked once someone starts to edit your entity but I don't see how you would get that with stored procedures as well.
All in all it took me about 2 solid days to get this all up and running for us.
Ok, each and every time I get into this situation, I struggle back and forth until I find a way to solve it (and that is usually not the way I would have liked to solve it).
What I'm talking about is disconnected entities in EF that should update existing entities in the database.
I'll give an example of my problem here (this example is the last time I got into this problem that caused me to write this question).
I have a WCF service that uses Entity Framework as well. The other program that have added a service reference to my service have gotten proxy versions of the Entities as normal.
The case is that the consumer of the service now construct a object of this proxy class, and call the method UpdateEntity on the WCF service. This entity has a foreign key to another type of entities, and the primary key of the entity I want to link this new entity to is also sent as a parameter to this method. In this case, I want the entity with the same primary key in the database to be updated. It seems simple enough right?
My method looks something like this now:
public bool ChangeEntity(MyEntity entity, int otherTableForignKey)
{
//first I verify that the entity to update exist in the system
var entitytochange = entityContext.MyEntities.FirstOrDefault(e => e.Name == entity.Name);
if (systemtochange == null) return false;
try
{
entity.ForignEntity = entityContext.ForeignEntities.FirstOrDefault(f => f.Key == otherTableForignKey);
//code for updating the entity should go here, but I'm nor sure what
entityContext.SaveChanges();
return true;
}
catch (Exception exc)
{
return false;
}
}
I tried many different combinations of ApplyCurrentValues, Attach, setting ObjectState to Modified and so on, but I get either the error message that I can't add a new entity with the same key as an existing entity, that the object state of the new object can't be Added and so on.
So my question is: What is the best way to do this without writing code that looks like a big hack.
The only way I got this working now was to just set the properties of entitytochange manually with the properties of entity, but it is a bad solution since any added properties to MyEntity will break the code if I don't remember to add code in this method as well, and it seems there really should be another way that is better.
EDIT
When I put entityContext.MyEntities.ApplyCurrentValues(entity); where my comment is put above, I get the following exception on this line:
The existing object in the ObjectContext is in the Added state. Changes can only be applied when the existing object is in an unchanged or modified state.
However, if I remove this line above entity.ForignEntity = entityContext.ForeignEntities.FirstOrDefault(f => f.Key == otherTableForignKey); then the ApplyCurrentValues works without any problems.
Why would me setting the ForeignEntity of the object set it to Added state? So it seems that setting a Property on the Detached entity, attaches it to the context with a state of added?
I need to write a row to the database regardless of whether it already exists or not. Before using NHibernate this was done with a stored procedure. The procedure would attempt an update and if no rows were modified it would fallback to an insert. This worked well because the application doesn't care if the record exists.
With NHibernate, the solutions I have found require loading the entity and modifying it, or deleting the entity so the new one can be inserted. The application does have to care if the record already exists. Is there a way around that?
Does the Id Matter?
Assigned Id
The object has a keyword as an assigned id and is the primary key in the table.
I understand that SaveOrUpdate() will call the Save() or Update() method as appropriate based on the Id. Using an assigned id, this won't work because the id isn't an unsaved-value. However a Version or Timestamp field could be used as an indicator instead. In reality, this isn't relevant because this only reflects on whether the object in memory has been associated with a record in the database; it does not indicate if the record exists or not in the database.
Generated Id
If the assigned id were truly the cause of the problem, I could use a generated id instead of the keyword as the primary key. This would avoid the NHibernate Insert/Update issue as it would effectively always insert. However, I still need to prevent duplicate keywords. With a unique index on the keyword column it will still throw an exception for a duplicate keyword even if the primary key is different.
Another Approach?
Perhaps the problem isn't really with NHibernate, but the way this is modeled. Unlike other areas of the application, this is more data-centric rather object-centric. It is nice that NHibernate makes it easy to read/write and eliminates the stored procedures. But the desire to simply write without regard to existing values doesn't fit well with the model of an object's identity model. Is there a better way to approach this?
I`m using
public IList<T> GetByExample<T>(T exampleInstance)
{
return _session.CreateCriteria(typeof(T))
.Add(Example.Create(exampleInstance))
.List<T>();
}
public void InsertOrUpdate<T>(T target)
{
ITransaction transaction = _session.BeginTransaction();
try
{
var res=GetByExample<T>(target);
if( res!=null && res.Count>0 )
_session.SaveOrUpdate(target);
else
_session.Save(target);
transaction.Commit();
}
catch (Exception)
{
transaction.Rollback();
throw;
}
finally
{
transaction.Dispose();
}
}
but FindByExample method returns all objects alike not objects with the exact ID what do you suggest ? since I have only object as parameter I don't have access to its specific ID field so I cannot use session.get(Object.class(), id);
Typically, NHibernate can rely on the unsaved-value to determine whether it should insert or create the entity. However, since you are assigning the ID, to NHibernate it looks like your entity has already been persisted. Therefore, you need to rely on versioning your object to let NHibernate know that it is a new object. See the following link for how to version your entity:
http://web.archive.org/web/20090831032934/http://devlicio.us/blogs/mike_nichols/archive/2008/07/29/when-flushing-goes-bad-assigned-ids-in-nhibernate.aspx
Use the session.SaveOrUpdate(object) method.
You can do
Obj j = session.get(Object.class(), id);
if (j != null)
session.merge(myObj);
else
session.saveOrUpdate(myObj);
Query objects where keyword = x, take FirstOrDefault. If it's null, Add new object, if it exists, update object that you got and call saveOrUpdate on it.
This worked for me:
Implementation
public void InsertOrUpdate<TEntity, TId>(TEntity entity) where TEntity : IIdentificableNh<TId>
{
var anyy = session.Get<TEntity>(entity.Id);
if (anyy != null)
{
session.Evict(anyy); //dispatch all data loaded, to allow updating 'entity' object.
session.Update(entity);
}
else
{
session.Save(entity);
}
session.Flush();
}
Entity
public class Caracteristica : IIdentificableNh<int>
{
public virtual int Id { get; set; }
public virtual string Descripcion { get; set; }
}
I had to create an interface (IIdentificableNh) that allows me to access the Id property value.
Usage example:
session.InsertOrUpdate<Caracteristica, int>(new Caracteristica { Id = 2, Descripcion = "Caracteristica2" });
call hibernate.saveOrUpdate() which will check if the object is in the database, update it if it is, and save (i.e. insert) it if it is not.