If I call Save on a new object, then populate its properties, NHibernate generates and insert statement that contains only the default values for the properties. For example (session is an open ISession):
var homer = new Person();
session.Save(homer);
homer.Name = "Homer J. Simpson";
session.Flush();
I thought that calling Save would make homer persistent and that NH would track any changes and include them in the insert. Instead, it issues an insert with the name property parameter set to null. If I put the Save call after the assignment then it works. This object has a GUID id assigned by NH so it's not doing a premature insert to get an identity.
ETA I'm using session-per-request in an ASP.NET app and the pattern I want to follow is:
MyObject myObject;
if (id == null)
{
myObject = new MyObject();
repository.Add(myObject);
}
else
{
myObject = repository.GetMyObject(id);
}
// populate myObject's properties
// NH magic happens here when the HTTP request ends
I think your assumption in this case is simply incorrect.
Reading the code sample you provided, you could just as well expect NHibernate to insert the object, and then subsequently change the Name and then issue an Update. That, however, would assume that Flush implicitly saves the changed state.
I also wonder why this happens. NH should really wait to insert the object to the database.
Reasons why could do this:
the id, you already said that you are using guids, so this shouldn't be the reason.
there is a query. To ensure that it is performed on actual data, the session is flushed.
there are calculated columns, which need to be read back from the database
there might be other reasons I don't remember.
Is this really the code you are running to reproduce the test?
How does the mapping file look like?
You just mentioned it in the answer to my (perhaps rather naive) comment. You have set session FlushMode to Auto. Change that to Manual and you're more likely to see the behavior you are seeking.
It's still a rather wild guess, simply because so many other properties of your configuration can be at play.
Related
I'm calling:
- (void)updateWithValues:(NSDictionary *)values
version:(uint64_t)version
in an NSIncrementalStore subclass in order to update the cache with update NSManagedObject values. My question concerns the values argument. Do I only need to put in the updated attributes or a complete new copy of the data?
The description in the documentation says: "Update the values and version to reflect new data being saved to or loaded from the external store. // The values dictionary is in the same format as the initializer."
It isn't clear to me whether or not the "values" that "reflect the new data" refers to only the updated attributes or all the attributes in the object.
It requires the complete data. I agree it wasn't very clear but I suppose the reason is so you can do the conflict handling first. The annoying thing is there is no way to get the values back from the node to merge in the new ones and set them again. Annoyingly this means you can't use the node as your cache object, I'm still learning the NSIncrementalStore so likely there reason for this design will come clear at some point.
I am attempting to use JMSSerializerBundle to consume JSON into Doctrine entities. I need to both create new entities where they do not already exist in the database, and update existing entities when they do already exist. I am using the DoctrineObjectConstructor included in the JMSSerializer package to help with this. When I consume JSON which contains a property designated as an identifier, such as:
{
"id": 1,
"some_other_attribute": "stuff"
}
by attempting to deserialize it, JMSSerializer causes warnings and eventually dies with an exception for attempting to utilize reflection to set properties on a null value. The warnings all look like this:
PHP Warning: ReflectionProperty::setValue() expects parameter 1 to be object, null given in /Users/cdonadeo/Repos/Ubertester/vendor/jms/serializer/src/JMS/Serializer/GenericDeserializationVisitor.php on line 176
If I manually insert an entity with ID 1 in my database and make another attempt then I receive no errors and everything appears to be working correctly, but I'm now short half my functionality. I looked at the code for the DoctrineObjectConstructor class, and at the top is a comment:
/**
* Doctrine object constructor for new (or existing) objects during deserialization.
*/
But I don't see how it could possibly create a new a new entity because after the construct() function has done all of its checks, at the end it calls:
$object = $objectManager->find($metadata->name, $identifierList);
And since the identifier does not exist in the database the result is null which is ultimately what gets returned from the function. This explains why inserting a row in the database with the appropriate ID makes things work: find() now returns a proper Entity object, which is what the rest of the library expects.
Am I using the library wrong or is it broken? I forked the Git repo and made an edit, and trying it out everything seems to work more or less the way I expected. That edit does have some drawbacks that make me wonder if I'm not just making this more difficult than it has to be. The biggest issue I see is that it will cause persisted and unpersisted entities to be mixed together with no way to tell which ones are which, but I don't know if that's even a big deal.
For Doctrine entities use configuration:
jms_serializer:
object_constructors:
doctrine:
fallback_strategy: "fallback" # possible values ("null" | "exception" | "fallback")
see configuration reference https://jmsyst.com/bundles/JMSSerializerBundle/master/configuration
I'm in the process of early research to replace EF with NHibernate in a system that is implemented using a custom written app engine.
The client creates an entity say, Person, gets the property values from the user and sends it to the server. In the server, we used context.CreateObject<Person>() to obtain a proxy of a Person.
Then the property values where applied to the proxy and we were able to Use Lazy loading to access related objects. For instance, if the person had a property MajorID and a navigation property Major, we set MajorID to 5 and if an expression accesses Major, the correct Major is lazily loaded into this field. A similar process happens for updates.
In NHibernate, I don't have a CreateOject<>() method, so the object I have is not proxied, and therefore lacks Lazy-Loading. Also, in Update, if I Change MajorID and then access Major, it still points to the old, wrong Major.
I'm quite new to NHibernate, can I have it behave like EF in this scenario?
Thanks
You don't need CreateObject at all in NHibernate.
The implementation of proxies in NH is completely different from EF, and it's based on entities, not properties.
Here's how this would work in NH:
var person = new Person(); //no proxy needed; person is a new entity
person.Major = session.Load<Major>(majorId); //creates Major proxy, no DB call
//...somewhere else
var majorId = person.Major.Id; //getting the Id does not cause loading, ever
var foo = person.Major.Foo; //this causes lazy-loading if not already loaded.
An interesting thing to note is that there is no MajorId property, nor there is need for one, because unlike EF, you can create proxies for already persisted entities.
I think you can achieve wat you use by session.Get<> and passing the ID of the person you want to load. For the id part, you generally should not works with it directly when you maniulate associations. Why dont you just try something like:
var p = session.Get<Person>(personId);
p.Major = session.Get<Majors>(mayorId);
session.Update(p);
I am using Model-Glue/Coldspring for a new application and I thought I would throw CF9 ORM into the mix.
The only issue I am having right now is with populating an entity with an object. More or less the code below verifies that only one username can exist. There is some other logic that is not displayed.
My first thought was to using something like this:
var entity = entityload('UserAccount' ,{UserName=arguments.UserAccount.getUserName()},"true")
entity = arguments.UserAccount;
How ever this does not work the way that I expected. Is it even possible to populate an entity with an object or do I need to use the setters?
Not sure if this is what you're looking for. If you have...
component persistent="true" entityName="Foo"
{
property a;
property b;
}
You can pass a struct in the 2nd param to init the entity (added in CF9.0.1 I believe)
EntityNew("Foo", {a="1",b="2"});
To populate Foo with another object, you can use the Memento pattern, and implement a GetMemento() function to your object that returns a struct of all its properties.
EntityNew("Foo", bar.getMemento());
However, CF does NOT call your custom setters! If you want to set them using setters, you may add calls to the setters in your init() constructor, or use your MVC framework of choice to populate the bean. In Model-Glue, it is makeEventBean().
Update: Or... Here's hack...
EntityNew("Foo", DeserializeJSON(SerializeJSON(valueObject)));
Use this at your own risk. JSON might do weird things to your numbers and the 'yes','no','true','false' strings. :)
Is it even possible to populate an entity with an object or do I need to use the setters?
If you mean "Is it possible to create load an ORM Entity from an instance of that persistent CFC that already exists and has properties set?", then yes you can using EntityLoadByExample( object,[unique] )
entity = EntityLoadByExample( arguments.userAccount,true );
This assumes the userAccount CFC has been defined as persistent, and its username value has been set before being passed in (which seems to be the case in your situation).
Bear in mind that if any other properties have been set in the object you are passing, including empty strings, they will be used as filters to load the entity, so if they do not exactly match a record in your database, nothing will be loaded.
The setup
Some of the "old old old" tables of our database use an exotic primary key generation scheme [1] and I'm trying to overlay this part of the database with NHibernate. This generation scheme is mostly hidden away in a stored procedure called, say, 'ShootMeInTheFace.GetNextSeededId'.
I have written an IIdentifierGenerator that calls this stored proc:
public class LegacyIdentityGenerator : IIdentifierGenerator, IConfigurable
{
// ... snip ...
public object Generate(ISessionImplementor session, object obj)
{
var connection = session.Connection;
using (var command = connection.CreateCommand())
{
SqlParameter param;
session.ConnectionManager.Transaction.Enlist(command);
command.CommandText = "ShootMeInTheFace.GetNextSeededId";
command.CommandType = CommandType.StoredProcedure;
param = command.CreateParameter() as SqlParameter;
param.Direction = ParameterDirection.Input;
param.ParameterName = "#sTableName";
param.SqlDbType = SqlDbType.VarChar;
param.Value = this.table;
command.Parameters.Add(param);
// ... snip ...
command.ExecuteNonQuery();
// ... snip ...
return ((IDataParameter)command
.Parameters["#sTrimmedNewId"]).Value as string);
}
}
The problem
I can map this in the XML mapping files and it works great, BUT....
It doesn't work when NHibernate tries to batch inserts, such as in a cascade, or when the session is not Flush()ed after every call to Save() on a transient entity that depends on this generator.
That's because NHibernate seems to be doing something like
for (each thing that I need to save)
{
[generate its id]
[add it to the batch]
}
[execute the sql in one big batch]
This doesn't work because, since the generator is asking the database every time, NHibernate just ends up getting the same ID generated multiple times, since it hasn't actually saved anything yet.
The other NHibernate generators like IncrementGenerator seem to get around this by asking the database for the seed value once and then incrementing the value in memory during subsequent calls in the same session. I would rather not do this in my implementation if I have to, since all of the code that I need is sitting in the database already, just waiting for me to call it correctly.
Is there a way to make NHibernate actually issue the INSERT after each call to generating an ID for entities of a certain type? Fiddling with the batch size settings don't seem to help.
Do you have any suggestions/other workarounds besides re-implementing the generation code in memory or bolting on some triggers to the legacy database? I guess I could always treat these as "assigned" generators and try to hide that fact somehow within the guts of the domain model....
Thanks for any advice.
The update: 2 months later
It was suggested in the answers below that I use an IPreInsertEventListener to implement this functionality. While this sounds reasonable, there were a few problems with this.
The first problem was that setting the id of an entity to the AssignedGenerator and then not actually assigning anything in code (since I was expecting my new IPreInsertEventListener implementation to do the work) resulted in an exception being thrown by the AssignedGenerator, since its Generate() method essentially does nothing but check to make sure that the id is not null, throwing an exception otherwise. This is worked around easily enough by creating my own IIdentifierGenerator that is like AssignedGenerator without the exception.
The second problem was that returning null from my new IIdentifierGenerator (the one I wrote to overcome the problems with the AssignedGenerator resulted in the innards of NHibernate throwing an exception, complaining that a null id was generated. Okay, fine, I changed my IIdentifierGenerator to return a sentinel string value, say, "NOT-REALLY-THE-REAL-ID", knowing that my IPreInsertEventListener would replace it with the correct value.
The third problem, and the ultimate deal-breaker, was that IPreInsertEventListener runs so late in the process that you need to update both the actual entity object as well as an array of state values that NHibernate uses. Typically this is not a problem and you can just follow Ayende's example. But there are three issues with the id field relating to the IPreInsertEventListeners:
The property is not in the #event.State array but instead in its own Id property.
The Id property does not have a public set accessor.
Updating only the entity but not the Id property results in the "NOT-REALLY-THE-REAL-ID" sentinel value being passed through to the database since the IPreInsertEventListener was unable to insert in the right places.
So my choice at this point was to use reflection to get at that NHibernate property, or to really sit down and say "look, the tool just wasn't meant to be used this way."
So I went back to my original IIdentifierGenreator and made it work for lazy flushes: it got the high value from the database on the first call, and then I re-implemented that ID generation function in C# for subsequent calls, modeling this after the Increment generator:
private string lastGenerated;
public object Generate(ISessionImplementor session, object obj)
{
string identity;
if (this.lastGenerated == null)
{
identity = GetTheValueFromTheDatabase();
}
else
{
identity = GenerateTheNextValueInCode();
}
this.lastGenerated = identity;
return identity;
}
This seems to work fine for a while, but like the increment generator, we might as well call it the TimeBombGenerator. If there are multiple worker processes executing this code in non-serializable transactions, or if there are multiple entities mapped to the same database table (it's an old database, it happened), then we will get multiple instances of this generator with the same lastGenerated seed value, resulting in duplicate identities.
##$##$#.
My solution at this point was to make the generator cache a dictionary of WeakReferences to ISessions and their lastGenerated values. This way, the lastGenerated is effectively local to the lifetime of a particular ISession, not the lifetime of the IIdentifierGenerator, and because I'm holding WeakReferences and culling them out at the beginning of each Generate() call, this won't explode in memory consumption. And since each ISession is going to hit the database table on its first call, we'll get the necessary row locks (assuming we're in a transaction) we need to prevent duplicate identities from happening (and if they do, such as from a phantom row, only the ISession needs to be thrown away, not the entire process).
It is ugly, but more feasible than changing the primary key scheme of a 10-year-old database. FWIW.
[1] If you care to know about the ID generation, you take a substring(len - 2) of all of the values currently in the PK column, cast them to integers and find the max, add one to that number, add all of that number's digits, and append the sum of those digits as a checksum. (If the database has one row containing "1000001", then we would get max 10000, +1 equals 10001, checksum is 02, resulting new PK is "1000102". Don't ask me why.
A potential workaround is to generate and assign the ID in an event listener rather than using an IIdentifierGenerator implementation. The listener should implement IPreInsertEventListener and assign the ID in OnPreInsert.
Why dont you just make private string lastGenerated; static?