Update documentation.

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>org.springframework.data</groupId>
 	<artifactId>spring-data-commons</artifactId>
-	<version>3.4.0-SNAPSHOT</version>
+	<version>3.4.0-3173-SNAPSHOT</version>
 
 	<name>Spring Data Core</name>
 	<description>Core Spring concepts underpinning every Spring Data module.</description>

src/main/antora/modules/ROOT/pages/repositories/core-concepts.adoc

@@ -4,6 +4,18 @@
 The central interface in the Spring Data repository abstraction is `Repository`.
 It takes the domain class to manage as well as the identifier type of the domain class as type arguments.
 This interface acts primarily as a marker interface to capture the types to work with and to help you to discover interfaces that extend this one.
+
+[TIP]
+====
+Spring Data considers domain types to be entities, more specifically aggregates.
+So you will see the term "entity" used throughout the documentation that can be interchanged with the term "domain type" or "aggregate".
+
+As you might have noticed in the introduction it already hinted towards domain-driven concepts.
+We consider domain objects in the sense of DDD.
+Domain objects have identifiers (otherwise these would be identity-less value objects), and we somehow need to refer to identifiers when working with certain patterns to access data.
+Referring to identifiers will become more meaningful as we talk about repositories and query methods.
+====
+
 The {spring-data-commons-javadoc-base}/org/springframework/data/repository/CrudRepository.html[`CrudRepository`] and {spring-data-commons-javadoc-base}/org/springframework/data/repository/ListCrudRepository.html[`ListCrudRepository`] interfaces provide sophisticated CRUD functionality for the entity class that is being managed.
 
 [[repositories.repository]]
@@ -37,6 +49,15 @@ public interface CrudRepository<T, ID> extends Repository<T, ID> {
 The methods declared in this interface are commonly referred to as CRUD methods.
 `ListCrudRepository` offers equivalent methods, but they return `List` where the `CrudRepository` methods return an `Iterable`.
 
+[IMPORTANT]
+====
+The repository interface implies a few reserved methods like `findById(ID identifier)` that target the domain type identifier property regardless of its property name.
+Read more about this in "`xref:repositories/query-methods-details.adoc#repositories.query-methods.reserved-methods[Defining Query Methods]`".
+
+You can annotate your query method with `@Query` to provide a custom query if a property named `Id` doesn't refer to the identifier.
+Following that path can easily lead to confusion and is discouraged as you will quickly hit type limits if the `ID` type and the type of your `Id` property deviate.
+====
+
 NOTE: We also provide persistence technology-specific abstractions, such as `JpaRepository` or `MongoRepository`.
 Those interfaces extend `CrudRepository` and expose the capabilities of the underlying persistence technology in addition to the rather generic persistence technology-agnostic interfaces such as `CrudRepository`.
 

src/main/antora/modules/ROOT/pages/repositories/query-keywords-reference.adoc

@@ -21,6 +21,22 @@ Consult the store-specific documentation for the exact list of supported keyword
 |`…Distinct…`| Use a distinct query to return only unique results. Consult the store-specific documentation whether that feature is supported. This keyword can occur in any place of the subject between `find` (and the other keywords) and `by`.
 |===============
 
+[[appendix.query.method.reserved]]
+== Reserved methods
+
+The following table lists reserved methods that use predefined functionality (as defined in `CrudRepository`).
+These methods are directly invoked on the backing (store-specific) implementation of the repository proxy.
+See also "`xref:repositories/query-methods-details.adoc#repositories.query-methods.reserved-methods[Defining Query Methods]`".
+
+.Reserved methods
+|===============
+|`deleteAllById(Iterable<ID> identifiers)`
+|`deleteById(ID identifier)`
+|`existsById(ID identifier)`
+|`findAllById(Iterable<ID> identifiers)`
+|`findById(ID identifier)`
+|===============
+
 [[appendix.query.method.predicate]]
 == Supported query method predicate keywords and modifiers
 

src/main/antora/modules/ROOT/pages/repositories/query-methods-details.adoc

@@ -86,6 +86,47 @@ Whether ignoring cases is supported may vary by store, so consult the relevant s
 - You can apply static ordering by appending an `OrderBy` clause to the query method that references a property and by providing a sorting direction (`Asc` or `Desc`).
 To create a query method that supports dynamic sorting, see "`xref:repositories/query-methods-details.adoc#repositories.special-parameters[Paging, Iterating Large Results, Sorting & Limiting]`".
 
+[[repositories.query-methods.reserved-methods]]
+== Reserved Method Names
+
+While derived repository methods bind to properties by name, there are a few exceptions to this rule when it comes to certain method names inherited from the base repository targeting the _identifier_ property.
+Those _reserved methods_ like `CrudRepository#findById` (or just `findById`) are targeting the _identifier_ property regardless of the actual property name used in the declared method.
+
+Consider the following domain type holding a property `pk` marked as the identifier via `@Id` and a property called `id`.
+In this case you need to pay close attention to the naming of your lookup methods as they may collide with predefined signatures:
+
+====
+[source,java]
+----
+class User {
+  @Id Long pk;                          <1>
+
+  Long id;                              <2>
+
+  // …
+}
+
+interface UserRepository extends Repository<User, Long> {
+
+  Optional<User> findById(Long id);     <3>
+
+  Optional<User> findByPk(Long pk);     <4>
+
+  Optional<User> findUserById(Long id); <5>
+}
+----
+
+<1> The identifier property (primary key).
+<2> A property named `id`, but not the identifier.
+<3> Targets the `pk` property (the one marked with `@Id` which is considered to be the identifier) as it refers to a `CrudRepository` base repository method.
+Therefore, it is not a derived query using of `id` as the property name would suggest because it is one of the _reserved methods_.
+<4> Targets the `pk` property by name as it is a derived query.
+<5> Targets the `id` property by using the descriptive token between `find` and `by` to avoid collisions with _reserved methods_.
+====
+
+This special behaviour not only targets lookup methods but also applies to the `exits` and `delete` ones.
+Please refer to the "`xref:repositories/query-keywords-reference.adoc#appendix.query.method.reserved[Repository query keywords]`" for the list of methods.
+
 [[repositories.query-methods.query-property-expressions]]
 == Property Expressions