Type-safe Kotlin query extension [DATAMONGO-2138]

[spring-projects-issues]

Tjeu opened DATAMONGO-2138 and commented

MongoTemplate already has many Kotlin extensions, and I'm suggesting to add extensions for "type-safe queries". This will prevent typos in field names, and improve the readability of a query.

The KMongo library uses Kotlin's Property References and infix functions for a type safe query syntax:

data class Jedi(val name: String)
val yoda = col.findOne(Jedi::name eq "Yoda")

https://github.com/Litote/kmongo/blob/master/kmongo-kdoc/docs/typed-queries.md

Spring Data MonoDB could provide a similar syntax:

val classic = Criteria("price").gt(1100)
    .and("available").isEqualTo(true)

val typed = typedCriteria {
    Book::price gt 1100
    Book::available isEqualTo true
}

assertEquals(classic, typed)

https://gist.github.com/TjeuKayim/91f52ae21bd5c33b99de028383d5ed89

I like to help coding this feature. It would be my first contribution to Spring

---

Reference URL: #622

Issue Links:

• DATAMONGO-2162 Add support for extended AND/OR query criteria using type-safe Kotlin queries
  ("is depended on by")
• DATAMONGO-2163 Type-safe Kotlin update extension
  ("is depended on by")
• DATAREST-1433 UnsatisfiedDependencyException with custom ID mapping in Kotlin

Referenced from: pull request #622

0 votes, 5 watchers

[spring-projects-issues]

Oliver Drotbohm commented

Sounds great to me. Maybe Sébastien Deleuze can advise?

[spring-projects-issues]

Sébastien Deleuze commented

Big +1 for that, and FYI this is an idea I would like to apply later to SQL for Spring Data JDBC and Spring Data R2DBC, so working on the Mongo side could help

[spring-projects-issues]

Tjeu commented

We can make the queries even more type safe with KProperty1.

The following function definition restricts the KProperty to members of the Entity class.

infix fun <T : Any> KProperty1<ENTITY, T>.isEqualTo(value: T)

// So the code below won't compile, because the classes don't match.
typedCriteria<Book>{ OtherClass::name isEqualTo "myBook"}

A disadvantage is that the generic type parameter "Book" has to be repeated in a call like this:

operations.find<Book>(Query(typedCriteria<Book> { Book::price gt 1100 }))

Query and CriteriaDefinition could be made generic, so that the generic parameter can be passed through to the typed query builder.

What do you think?

[spring-projects-issues]

Tjeu commented

Making Query and CriteriaDefinition generic won't be backward compatible. So it is not really a good idea

[spring-projects-issues]

Mark Paluch commented

I filed  DATAMONGO-2162 and DATAMONGO-2163 to continue on query operators and Update support