Missing way to locate by EntityId

[jansorg]

I couldn't find a way to load an XdEntity by EntityId (a string with a value of an EntityId).

I guess that there's a better way, but here's my code to to this:

import kotlinx.dnq.XdEntity
import kotlinx.dnq.XdNaturalEntityType

open class XdCustomEntityType<T : XdEntity>() : XdNaturalEntityType<T>(storeContainer = ThreadLocalStoreContainer) {
    fun find(id: String): T? {
        val transaction = (XdOrganisation.entityStore.threadSession
                ?: throw IllegalStateException("New entities can be created only in transactional block"))

        val entity = transaction.getEntity(transaction.toEntityId(id))
        return wrap(entity).apply {
            constructor()
        }
    }
}

[sedovalx]

EntityId is a low level class. Why do you need to search by it? Usually, you have an identity field in a base class of your xd-hierarchy:

abstract class XdIdEntityType<XD : XdIdEntity> : XdNaturalEntityType<XD>(ThreadLocalStoreContainer) {
    fun findById(id: Long): XD? {
        return all().firstOrNull(XdIdEntity::id eq id)
    }
}

abstract class XdIdEntity(entity: Entity) : XdEntity(entity) {
    companion object : XdIdEntityType<XdIdEntity>()
    
    val id by xdRequiredLongProp(unique = true) { min(0) }
}

And there is a kind of agreement that all operations over xd-entities that involve data reads or writes should be done in a transactional block. So, typically, there is no need to check the current transaction in xd-methods.
Anyway, you are on a right way if you think you need to search by an EntityId. Here is how I would do it:

val store: TransientEntityStore = TODO()
val entityId: String = TODO()
        
store.transactional { txn ->
    txn.getEntity(txn.toEntityId(entityId)).toXd<XdMyEntity>()
}

[jansorg]

Thanks @sedovalx ,
I couldn't find a way to have an automatically generated UUID in my entities, so I used the internal id (as suggest at https://github.com/JetBrains/xodus/wiki/Entity-Stores#entities at the end).

I'm now using a halfway automatic solution using UUIDs and a find operation like you suggested.

[sedovalx]

You can use UUID.randomUUID().toString() in a constructor of your xd-entities:

abstract class XdIdEntityType<XD : XdIdEntity> : XdNaturalEntityType<XD>(ThreadLocalStoreContainer) {
    fun findById(id: String): XD? {
        return all().firstOrNull(XdIdEntity::id eq id)
    }
}

abstract class XdIdEntity(entity: Entity) : XdEntity(entity) {
    companion object : XdIdEntityType<XdIdEntity>()

    var id by xdRequiredStringProp(unique = true, trimmed = true)

    override fun constructor() {
        this.id = UUID.randomUUID().toString()
    }

    override fun beforeFlush() {
        if (!isNew && hasChanges(XdIdEntity::id)) {
            throw DataConstraintsException("It is not allowed to change ID after construction")
        }
    }
}

class XdMyEntity(entity: Entity) : XdIdEntity(entity) {
    companion object : XdIdEntityType<XdMyEntity>() {
        fun new(value: Int) = new {
            this.value = value
        }
    }

    override fun constructor() {
        super.constructor()
        this.defaultProp = "default value"
    }

    var value by xdIntProp()
    var defaultProp by xdStringProp()
}

And then val xd = XdMyEntity.new(42).

[lehvolk]

@sedovalx EntityId is a reliable database identity which can be used as unique entity identity across single database. At the moment we have only one implementation of EntityId for which toString will return string identity like typeId-entityLocalId. Backward API is not supported in xodus-dnq at the moment thus you should make a low-level call tx.getEntity(tx.toEntityId(entityStringId)).toXd().

I think we should definitely support converting EntityId to String and back and type safe search by id across database.