Introduce first-class type-safe property path references at the core level

[mp911de]

We now support type-safe property paths and property references:

Java variants:

PropertyPath.from("name", Person.class) // existing String-based API
PropertyPath.of(Person::getName) // type-safe property reference expression

PropertyPath.from("address.country", Person.class) // existing nested path API
PropertyPath.of(Person::getAddress).then(Address::getCountry) // type-safe composed path expression


PropertyReference.of(Secret::getSecret)

Kotlin variants:

PropertyReference.of(Secret::secret)

PropertyPath.of(Person::address / Address::city)

allowing type-safe usage through e.g.:

Sort.by(Person::getFirstName, Person::getLastName)

Module adoption:

• Introduce Expressions utility for type-safe Criteria Query Expression resolution spring-data-jpa#4086
• Use TypedPropertyPaths spring-data-mongodb#5135
• Relational
• Retrofit Query and Update API accepting TypedPropertyPath spring-data-cassandra#1626

[schauder]

Looks great. I left a few nitpicks.

I didn't look into actually using it, since it seems Christoph already did that.
Let me know if I should take it for a spin as well.

[schauder]

can we make org.springframework.data.core a link into the package overview in the JavaDoc?

[schauder]

can we make org.springframework.data.core a link into the package overview in the JavaDoc?

[schauder]

"one to many segments"

I know, I lost the fight before, but I still find it really weird, that we don't have zero length paths, referring to the a aggregate root itself.

[schauder]

"The following examples express the same intent" hints at a comparison with a text base definition of the same property path. We should either explicitly reference the example used above, or include the text based version here again in the example.

[schauder]

"The following examples express the same intent" hints at a comparison with a text base definition of the same property path. We should either explicitly reference the example used above, or include the text based version here again in the example.

[schauder]

I find this title a little confusing, because it seems to match the previous example much better than this one.

In general we should probably decide if we want titles with our examples or not and make all examples match that style.

[schauder]

The last one should be just name, instead of city.name

[schauder]

Could we improve readability a little by using something more mnemonic than T? Or am I missing something?

O for Orgin or Owner.
R for Root
S for Source

Applies also for TypedPropertyPath

[schauder]

Why are we mapping it explicitly to TypedPropertyPath? This happens already in the getSegment called inside toDotPath.

If this is for performance reasons (just guessing) we should add a comment to that effect .

[schauder]

This pattern appears a couple of times.

[schauder]

I'm a little confused by the name TCK. This seems more like a PropertyPathTestSupport.

From a TCK I would expect that it actually forces you to provide certain propertyPaths.
Maybe as a Map from a String representation to the representation under test and then run a bunch of tests against these, and failing when expected paths aren't in the provided Map.