# Object Repository

ObjectRepository provides a simple and type-safe API for storing and retrieving Kotlin/Java objects in a Nitrite database. It is built on top of NitriteCollection and provides a similar API for CRUD operations. It also supports indexing and querying. It also supports event based notification on object changes.

More details on repository can be found here.

Potassium Nitrite provides some higher-order functions to make repository manipulation easier.

You can create a ObjectRepository by passing a class type to getRepository() method.

val repository = db.getRepository<Employee>() {
    // do something with repository
    insert(Employee("John", "Doe"))
    createIndex("firstName")
}

You can create a keyed ObjectRepository by passing a class type and a key to getRepository() method.

val repository = db.getRepository<Employee>("myKey") {
    // do something with repository
    insert(Employee("John", "Doe"))
    createIndex("firstName")
}

One typical use case of this keyed repository is to create a repository for each user in a multi-user application. The key can be the user name or user id. This will ensure that each user will have a separate repository for storing objects.

A ObjectRepository can be created using EntityDecorator. This is useful when you cannot modify the object class to add annotations.

More details about EntityDecorator can be found here.

val repository = db.getRepository(EmployeeDecorator()) {
    // do something with repository
    insert(Employee("John", "Doe"))
    createIndex("firstName")
}

A keyed ObjectRepository can be created using EntityDecorator and a key. This is useful when you cannot modify the object class to add annotations.

More details about EntityDecorator can be found here.

val repository = db.getRepository(EmployeeDecorator(), "myKey") {
    // do something with repository
    insert(Employee("John", "Doe"))
    createIndex("firstName")
}

Nitrite provides a mapper interface called NitriteMapper. It is used to map Java objects to Nitrite documents and vice-versa. More details on NitriteMapper can be found here.

Apart from the SimpleNitriteMapper, Potassium Nitrite also provides two additional mappers:

• KNO2JacksonMapper
• KotlinXSerializationMapper

Potassium Nitrite extends the JacksonMapper to provide KNO2JacksonMapper. This class overrides the getObjectMapper() method to register some Kotlin specific Jackson modules as follows:

• KotlinModule
• JavaTimeModule
• Jdk8Module
• GeometryModule

It also disables the SerializationFeature.WRITE_DATES_AS_TIMESTAMPS feature. The constructor of KNO2JacksonMapper takes a vararg of com.fasterxml.jackson.databind.Module to register additional Jackson modules.

To use the KNO2JacksonMapper instead of the default SimpleNitriteMapper you need to load it while opening the database.

val db = nitrite {
    loadModule(module(KNO2JacksonMapper()))
}

Potassium Nitrite also provides a KotlinX Serialization based mapper called KotlinXSerializationMapper. KotlinX Serialization is used to convert Java/Kotlin objects to Document and vice-versa.

To use the KotlinXSerializationMapper instead of the default SimpleNitriteMapper you need to load it while opening the database.

val db = nitrite {
    loadModule(module(KotlinXSerializationMapper()))
}