I'm trying to write a simple REST API in a Reactive way (using R2DBC) with all CRUD operations on a database storing books. With one of the defined endpoints it should be possible to save a book to the database. So I have written the following code to save a book to the database:
public Mono<Book> saveBook(Mono<Book> book) throws ResourceAlreadyExistsException {
return book.doOnNext(b -> log.info("Save book with title " + b.toString()))
.flatMap(b -> bookRepository.findByTitle(b.getTitle()))
.switchIfEmpty(Mono.defer(() -> bookRepository.saveAll(book).next()))
.flatMap(b -> Mono.error(
new ResourceAlreadyExistsException(String.format("Book already exists for provided title :: %s" , book.getTitle()))));
}
So I first check if the book title already exists in the database. If the book does not exists, the switchIfEmpty will be executed, and the book will be stored. But after the switchIfEmpty, the flatMap is also always called! In the above code, even when a book is stored successfully, an error will be thrown in the last flatmap. Obviously I am doing something wrong here...
What I am trying to achieve in my reactive application is the following:
Check if the book title already exists in the database
If not, save the book to the database
If the book already exists, throw an exception
I hope someone can help to write this piece of code in a clean and efficient way!
I think the most effective way to do it is by using constraints in your database. If you set the title as a unique column and you try to save another book with the same title, the database will throw the exception.
The only thing you have to do then is to "catch" this exception with the onErrorResume method and convert it to your custom "ResourceAlreadyExists" exception.
Related
I am wondering if it is possible to map a named native query on the fly instead of getting back a list of Object[] and then looping through and setting up the object that way. I have a call which I know ill return a massive data set and I want to be able to map it right to my entity. Can I do that or will I have to continue looping through the result set.
Here is what I am doing now...
List<Provider> ObjList = (List<Provider>) emf.createNativeQuery(assembleQuery(organizationIDs, 5)).getResultList();
That is my entity, the List (my entity is the provider). Normally I would just return a List<Object[]>
and then I would loop through that to get back all the objects and set them up as new providers and add them to a list....
//List<Provider> provList = new ArrayList<Provider>();
/*for(Object[] obj: ObjList)
{
provList.add(this.GetProviderFromObj(obj));
}*/
As you can see I commented that section of the code out to try this out. I know you can map named native queries if you put your native query in the entity itself and then call it via createNamedQuery. I would do it that way, but I need to use the IN oracle keyword because I have a list of ID's that I want to check against. It is not just one that is needed. And as we all know, native queruies don't handle the in keyword to well. Any advice?
Sigh, If only the IN keyword was supported well for NamedNativeQueries.
Assuming that Provider is configured as a JPA entity, you should be able to specify the class as the second parameter to your createNativeQuery call. For example:
List<Provider> ObjList = (List<Provider>) emf.createNativeQuery(assembleQuery(organizationIDs, 5), Provider.class).getResultList();
According to the documentation, "At a minimum, your SQL must select the class' primary key columns, discriminator column (if mapped), and version column (also if mapped)."
See the OpenJPA documentation for more details.
I want to add property to existing document (using clues form http://ravendb.net/docs/client-api/partial-document-updates). But before adding want to check if that property already exists in my database.
Is any "special,proper ravendB way" to achieve that?
Or just load document and check if this property is null or not?
You can do this using a set based database update. You carry it out using JavaScript, which fortunately is similar enough to C# to make it a pretty painless process for anybody. Here's an example of an update I just ran.
Note: You have to be very careful doing this because errors in your script may have undesired results. For example, in my code CustomId contains something like '1234-1'. In my first iteration of writing the script, I had:
product.Order = parseInt(product.CustomId.split('-'));
Notice I forgot the indexer after split. The result? An error, right? Nope. Order had the value of 12341! It is supposed to be 1. So be careful and be sure to test it thoroughly.
Example:
Job has a Products property (a collection) and I'm adding the new Order property to existing Products.
ravenSession.Advanced.DocumentStore.DatabaseCommands.UpdateByIndex(
"Raven/DocumentsByEntityName",
new IndexQuery { Query = "Tag:Jobs" },
new ScriptedPatchRequest { Script =
#"
this.Products.Map(function(product) {
if(product.Order == undefined)
{
product.Order = parseInt(product.CustomId.split('-')[1]);
}
return product;
});"
}
);
I referenced these pages to build it:
set based ops
partial document updates (in particular the Map section)
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've got an Account model object and a UNIQUE constraint on the account's Name. In Domain Driven Design, using nHibernate, how should I check for the name's unicity before inserting or updating an entity?
I don't want to rely on a nHibernate exception to catch the error. I'd like to return a prettier error message to my user than the obscure could not execute batch command.[SQL: SQL not available]
In the question Where should I put a unique check in DDD?, someone suggested using a Specification like so.
Account accountA = _accountRepository.Get(123);
Account accountB = _accountRepository.Get(456);
accountA.Name = accountB.Name;
ISpecification<Account> spec = new Domain.Specifications.UniqueNameSpecification(_accountRepository);
if (spec.IsSatisfiedBy(accountObjA) == false) {
throw new Domain.UnicityException("A duplicate Account name was found");
}
with the Specification code as:
public bool IsSatisfiedBy(Account obj)
{
Account other = _accountRepository.GetAccountByName(obj.Name);
return (other == null);
}
This works for inserts, but not when doing an update because. I tried changing the code to:
public bool IsSatisfiedBy(Account obj)
{
Account other = _accountRepository.GetAccountByName(obj.Name);
if (obj == null) { // nothing in DB
return true;
}
else { // must be the same object.
return other.Equals(obj);
}
}
The problem is that nHibernate will issue an update to the database when it executes GetAccountByName() to recover a possible duplicate...
return session.QueryOver<Account>().Where(x => x.Name == accntName).SingleOrDefault();
So, what should I do? Is the Specification not the right way to do it?
Thanks for your thoughts!
I'm not a fan of the specification pattern for data access, it always seems like jumping hoops to get anything done.
However, what you've suggested, which really just boils down to:
Check if it already exists.
Add if it doesn't; Show user-friendly message if it does.
... is pretty much the easiest way to get it done.
Relying on database exceptions is the other way of doing it, if your database and it's .NET client gracefully propagates the table & column(s) that were infringing the unique constraint. I believe most drivers don't do so (??), as they just throw a generic ConstraintException that says "Constraint XYZ was violated on table ABC". You can of course have a convention on your unique constraint naming to say something like UK_MyTable_MyColumn and do string magic to pull the table & column names out.
NHibernate has a ISQLExceptionConverter that you can plug into the Configuration object when you set NHibernate up. Inside this, you get exposed to the exception from the .NET data client. You can use that exception to extract the table & columns (using the constraint name perhaps?) and throw a new Exception with a user friendly message.
Using the database exception way is more performant and you can push a lot of the detecting-unique-constraint-violation code to the infrastructure layer, as opposed to handling each one case by case.
Another thing worth pointing out with the query-first-then-add method is that to be completely transaction safe, you need to escalate the transaction level to serializable (which gives the worst concurrency) to be totally bullet proof. Whether you need to be totally bullet proof or not, depends on your application needs.
You need to handle it with Session.FlushMode mode to set to FlushMode.Commit and use transaction to rollback if at all update fired.
I am going through the RavenDB tutorial on the RavenDb.net website.
It was going fine until I got to the code block for creating an index.
This code segment is direct from RavenDB.Net website.
store.DatabaseCommands.PutIndex("OrdersContainingProduct", new IndexDefinition<Order>
{
Map = orders => from order in orders
from line in order.OrderLines
select new { line.ProductId }
});
I get an error on compile: "The non-generic type 'Raven.Database.Indexing.IndexDefinition' cannot be used with type arguments."
If IndexDefinition is non-generic, why is it used as generic in the sample code? Where is the disconnect?
Thank you for your time
Jim
Depending on your using statements you may be referencing the wrong IndexDefinition class (from another Raven assembly). Try adding this to the beginning of your file:
using Raven.Client.Indexes;
You might need to remove other using statements as well. I guess this is one reason why Microsoft recommends using unique names for classes even in the presence of namespaces.