DATACMNS-1699 - Add Embedded annotation.

[christophstrobl]

Add core annotation for embedded object support and consider a potential prefix when using FieldNamingStrategies.

The actual store specific implementation is done in the individual modules that make sure the mapping context provides means to detect embedded types and provide this information to the PersistentPropertyPathFactory now using PersistentEntitiesinstead of theTypeInformation` to construct mapped paths.

[schauder]

When a property is not embedded, it is never nullable. If that is intended, it should be described in the documentation and the superfluous parens around the first && term should be removed.

Or the expression should get fixed. Also we should have tests for the not embedded case.

[dcominottim]

It'd be really nice if we could further customize this annotation with more parameters or pair it with another annotation to achieve the same effect from @Embedded + @AttributeOverride from javax.persistence. This way, the name of the inline fields could be customized in/by the parent object and the embeddable objects could be more re-used. (Real world example: I need such customization to create [DDD] Value Objects that can be re-used in/by different entities/documents when using MongoDB.)

[mp911de]

Embedded objects are conceptually stable regarding their property to field/column/… names. @Embedded allows you to provide a prefix to customize physical naming. An example use-case:

class Address {
  String street, city;
}

class Order {

  @Embedded(prefix = "shipping_")
  Address shipping;

  @Embedded(prefix = "billing_")
  Address billing;
}

Rendering fields shipping_street, shipping_city, billing_street, and so on.

@dcominottim care to elaborate how else you'd like to customize field names?

[dcominottim]

Embedded objects are conceptually stable regarding their property to field/column/… names. @Embedded allows you to provide a prefix to customize physical naming. An example use-case:

class Address {
  String street, city;
}

class Order {

  @Embedded(prefix = "shipping_")
  Address shipping;

  @Embedded(prefix = "billing_")
  Address billing;
}

Rendering fields shipping_street, shipping_city, billing_street, and so on.

@dcominottim care to elaborate how else you'd like to customize field names?

Thanks for the reply, @mp911de. I had overlooked the 'prefix' param. It seems to work mostly fine for embedded objects that aggregate multiple properties (such as your Address example). I think it should often work for value objects that encapsulate a single property as well (e.g.: class CompanyName { String companyName; }), although it'd still be useful for the parent to be able to fully override that -- in JPA, it'd be

class Company {
  @Embedded
  @AttributeOverride(
    name = "companyName", // name of the target attribute
    column = @Column(name = "CMP_NAME") // name that will be used for persistence
  )
  CompanyName name;
}

Think of a scenario in which the company you work for has complex rules for data modeling and the data governance team may request you to use specific column/attribute names for certain tables/documents -- and they don't play well with Java/Spring Data attribute naming conventions. I am in such scenario right now and need to use @AttributeOverride in JPA projects with strong object orientation/encapsulation/DDD patterns.

On a separate note, does Spring Data fully support underscore in attribute names nowadays (as per your prefix example)? It didn't use to. Sorry if too obvious. #126

[oooplz]

Thank you for open source contribution. The feature still be watched?

[mp911de]

Superseded by #2294.