Question

I have entity structure like this:

base class EntityBase with Key field Id (type of long) child classes: Person and Material both are inherited from EntityBase

i have copied sql database from one pc to another (by sql export procedure) and as a result (after some time program work and creates some entities) i have a situation when dbo.Person and dbo.Material tables contains rows with same Id 1921. Now when i'm trying to query for Session.Query.Single<person>(1921) - this code throws exception:

Entity with Key = 'Material (unknown), (1921)' does not exist.

stacktrace:

Xtensive.Orm.QueryEndpoint.Single(Key key)
Xtensive.Orm.QueryEndpoint.Single[T](Object[] keyValues)
Teleavtomatika.Practices.DataObjects.DtoBase`1.GetEntity() 
Teleavtomatika.Practices.DataObjects.DtoBase`1.Teleavtomatika.Practices.DataObjects.IDtoBase.GetEntity() 
Teleavtomatika.Practices.DataObjects.DtoBase`1.TransferDataToEntity(T entity, HashSet`1 cache) 
Teleavtomatika.Practices.DataObjects.DtoSet`1.Merge[TEntity,TDto](EntitySet`1 entitySet, DtoSet`1 dtoSet, HashSet`1 cache)

So my question is: where does DO stores information about last Key (ID) generated and how can i eliminate the situation when two different types of entities inherited from the same base entity class can have same Id?

My DO version is 4.5.5.

Answer 1

Hello Dmitry F.

According to key providing behavior keys of two entity can't be the same. I thing something went wrong when you did export procedure. Generally, keys are generated by special table in database which name is <name of="" keys'="" type="">-Generator or some custom name for custom generators. It have only one field with auto increment. Sometimes if DBMS supports sequences then DO use it. As I know, DO uses sequences for MS SQL Server 2012 and PostgreSql and Oracle. I suppose something happened with generator table or sequence.

You can define key generator parameters in domain configuration.

Using AppConfig in <domain> element:


<keyGenerators>
 <!-- Seed and cache size values are just for example -->
      <keyGenerator name="Int32" database="main" seed="128" cacheSize="128"/>
</keyGenerators>

or using DomainConfiguration.KeyGenerators collection


//Cache size and seed values are just for example.
domainConfiguration.KeyGenerators.Add(new KeyGeneratorConfiguration("Int32") {CacheSize = 128, Seed = 128});//for Int32 keys
domainConfiguration.KeyGenerators.Add(new KeyGeneratorConfiguration("Int64") {CacheSize = 128, Seed = 128000});// for Int64 (long) keys

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