Implement Query by Example.

Implement Spring Data's Query by Example feature.

See #532 and spring-projects/spring-data-relational#929.

Author: lub2code

Diff for: pom.xml

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
 
 	<modelVersion>4.0.0</modelVersion>
 

Diff for: src/main/asciidoc/new-features.adoc

@@ -1,6 +1,11 @@
 [[new-features]]
 = New & Noteworthy
 
+[[new-features.1-3-0]]
+== What's New in Spring Data R2DBC 1.3.0
+
+* Introduce <<r2dbc.repositories.queries.query-by-example,Query by Example support>>.
+
 [[new-features.1-2-0]]
 == What's New in Spring Data R2DBC 1.2.0
 

Diff for: src/main/asciidoc/reference/r2dbc-repositories.adoc

@@ -279,6 +279,47 @@ Extensions are retrieved from the application context at the time of SpEL evalua
 
 TIP: When using SpEL expressions in combination with plain parameters, use named parameter notation instead of native bind markers to ensure a proper binding order.
 
+[[r2dbc.repositories.queries.query-by-example]]
+=== Query By Example
+
+Spring Data R2DBC also lets you use Query By Example to fashion queries.
+This technique allows you to use a "probe" object.
+Essentially, any field that isn't empty or `null` will be used to match.
+
+Here's an example:
+
+====
+[source,java,indent=0]
+----
+include::../{example-root}/QueryByExampleTests.java[tag=example]
+----
+<1> Create a domain object with the criteria (`null` fields will be ignored).
+<2> Using the domain object, create an `Example`.
+<3> Through the `R2dbcRepository`, execute query (use `findOne` for a `Mono`).
+====
+
+This illustrates how to craft a simple probe using a domain object.
+In this case, it will query based on the `Employee` object's `name` field being equal to `Frodo`.
+`null` fields are ignored.
+
+====
+[source,java,indent=0]
+----
+include::../{example-root}/QueryByExampleTests.java[tag=example-2]
+----
+<1> Create a custom `ExampleMatcher` that matches on ALL fields (use `matchingAny()` to match on *ANY* fields)
+<2> For the `name` field, use a wildcard that matches against the end of the field
+<3> Match columns against `null` (don't forget that `NULL` doesn't equal `NULL` in relational databases).
+<4> Ignore the `role` field when forming the query.
+<5> Plug the custom `ExampleMatcher` into the probe.
+====
+
+It's also possible to apply a `withTransform()` against any property, allowing you to transform a property before forming the query.
+For example, you can apply a `toUpperCase()` to a `String` -based property before the query is created.
+
+Query By Example really shines when you you don't know all the fields needed in a query in advance.
+If you were building a filter on a web page where the user can pick the fields, Query By Example is a great way to flexibly capture that into an efficient query.
+
 [[r2dbc.entity-persistence.state-detection-strategies]]
 === Entity State Detection Strategies
 

Diff for: src/main/java/org/springframework/data/r2dbc/repository/R2dbcRepository.java

@@ -16,13 +16,15 @@
 package org.springframework.data.r2dbc.repository;
 
 import org.springframework.data.repository.NoRepositoryBean;
+import org.springframework.data.repository.query.ReactiveQueryByExampleExecutor;
 import org.springframework.data.repository.reactive.ReactiveSortingRepository;
 
 /**
  * R2DBC specific {@link org.springframework.data.repository.Repository} interface with reactive support.
  *
  * @author Mark Paluch
  * @author Stephen Cohen
+ * @author Greg Turnquist
  */
 @NoRepositoryBean
-public interface R2dbcRepository<T, ID> extends ReactiveSortingRepository<T, ID> {}
+public interface R2dbcRepository<T, ID> extends ReactiveSortingRepository<T, ID>, ReactiveQueryByExampleExecutor<T> {}

Diff for: src/main/java/org/springframework/data/r2dbc/repository/support/SimpleR2dbcRepository.java

@@ -21,16 +21,18 @@
 import java.util.List;
 
 import org.reactivestreams.Publisher;
-
+import org.springframework.data.domain.Example;
 import org.springframework.data.domain.Sort;
 import org.springframework.data.r2dbc.convert.R2dbcConverter;
 import org.springframework.data.r2dbc.core.R2dbcEntityOperations;
 import org.springframework.data.r2dbc.core.R2dbcEntityTemplate;
 import org.springframework.data.r2dbc.core.ReactiveDataAccessStrategy;
+import org.springframework.data.r2dbc.repository.R2dbcRepository;
 import org.springframework.data.relational.core.mapping.RelationalPersistentProperty;
 import org.springframework.data.relational.core.query.Criteria;
 import org.springframework.data.relational.core.query.Query;
 import org.springframework.data.relational.repository.query.RelationalEntityInformation;
+import org.springframework.data.relational.repository.query.RelationalExampleMapper;
 import org.springframework.data.repository.reactive.ReactiveSortingRepository;
 import org.springframework.data.util.Lazy;
 import org.springframework.data.util.Streamable;
@@ -45,13 +47,15 @@
  * @author Jens Schauder
  * @author Mingyuan Wu
  * @author Stephen Cohen
+ * @author Greg Turnquist
  */
 @Transactional(readOnly = true)
-public class SimpleR2dbcRepository<T, ID> implements ReactiveSortingRepository<T, ID> {
+public class SimpleR2dbcRepository<T, ID> implements R2dbcRepository<T, ID> {
 
 	private final RelationalEntityInformation<T, ID> entity;
 	private final R2dbcEntityOperations entityOperations;
 	private final Lazy<RelationalPersistentProperty> idProperty;
+	private final RelationalExampleMapper exampleMapper;
 
 	/**
 	 * Create a new {@link SimpleR2dbcRepository}.
@@ -70,6 +74,7 @@ public SimpleR2dbcRepository(RelationalEntityInformation<T, ID> entity, R2dbcEnt
 				.getMappingContext() //
 				.getRequiredPersistentEntity(this.entity.getJavaType()) //
 				.getRequiredIdProperty());
+		this.exampleMapper = new RelationalExampleMapper(converter.getMappingContext());
 	}
 
 	/**
@@ -90,6 +95,7 @@ public SimpleR2dbcRepository(RelationalEntityInformation<T, ID> entity, Database
 				.getMappingContext() //
 				.getRequiredPersistentEntity(this.entity.getJavaType()) //
 				.getRequiredIdProperty());
+		this.exampleMapper = new RelationalExampleMapper(converter.getMappingContext());
 	}
 
 	/**
@@ -112,6 +118,7 @@ public SimpleR2dbcRepository(RelationalEntityInformation<T, ID> entity,
 				.getMappingContext() //
 				.getRequiredPersistentEntity(this.entity.getJavaType()) //
 				.getRequiredIdProperty());
+		this.exampleMapper = new RelationalExampleMapper(converter.getMappingContext());
 	}
 
 	// -------------------------------------------------------------------------
@@ -372,6 +379,59 @@ public Flux<T> findAll(Sort sort) {
 		return this.entityOperations.select(Query.empty().sort(sort), this.entity.getJavaType());
 	}
 
+	// -------------------------------------------------------------------------
+	// Methods from ReactiveQueryByExampleExecutor
+	// -------------------------------------------------------------------------
+
+	@Override
+	public <S extends T> Mono<S> findOne(Example<S> example) {
+
+		Assert.notNull(example, "Example must not be null!");
+
+		Query query = this.exampleMapper.getMappedExample(example);
+
+		return this.entityOperations.selectOne(query, example.getProbeType());
+	}
+
+	@Override
+	public <S extends T> Flux<S> findAll(Example<S> example) {
+
+		Assert.notNull(example, "Example must not be null!");
+
+		return findAll(example, Sort.unsorted());
+	}
+
+	@Override
+	public <S extends T> Flux<S> findAll(Example<S> example, Sort sort) {
+
+		Assert.notNull(example, "Example must not be null!");
+		Assert.notNull(sort, "Sort must not be null!");
+
+		Query query = this.exampleMapper.getMappedExample(example).sort(sort);
+
+		return this.entityOperations.select(query, example.getProbeType());
+	}
+
+	@Override
+	public <S extends T> Mono<Long> count(Example<S> example) {
+
+		Assert.notNull(example, "Example must not be null!");
+
+		Query query = this.exampleMapper.getMappedExample(example);
+
+		return this.entityOperations.count(query, example.getProbeType());
+	}
+
+	@Override
+	public <S extends T> Mono<Boolean> exists(Example<S> example) {
+
+		Assert.notNull(example, "Example must not be null!");
+
+		Query query = this.exampleMapper.getMappedExample(example);
+
+		return this.entityOperations.exists(query, example.getProbeType());
+	}
+
 	private RelationalPersistentProperty getIdProperty() {
 		return this.idProperty.get();
 	}

Diff for: src/test/java/org/springframework/data/r2dbc/documentation/QueryByExampleTests.java

@@ -0,0 +1,65 @@
+package org.springframework.data.r2dbc.documentation;
+
+import static org.springframework.data.domain.ExampleMatcher.*;
+import static org.springframework.data.domain.ExampleMatcher.GenericPropertyMatchers.*;
+
+import lombok.Data;
+import lombok.NoArgsConstructor;
+import reactor.core.publisher.Flux;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.data.annotation.Id;
+import org.springframework.data.domain.Example;
+import org.springframework.data.domain.ExampleMatcher;
+import org.springframework.data.r2dbc.repository.R2dbcRepository;
+
+public class QueryByExampleTests {
+
+	private EmployeeRepository repository;
+
+	@Test
+	void queryByExampleSimple() {
+
+		// tag::example[]
+		Employee employee = new Employee(); // <1>
+		employee.setName("Frodo");
+
+		Example<Employee> example = Example.of(employee); // <2>
+
+		Flux<Employee> employees = repository.findAll(example); // <3>
+
+		// do whatever with the flux
+		// end::example[]
+	}
+
+	@Test
+	void queryByExampleCustomMatcher() {
+
+		// tag::example-2[]
+		Employee employee = new Employee();
+		employee.setName("Baggins");
+		employee.setRole("ring bearer");
+
+		ExampleMatcher matcher = matching() // <1>
+				.withMatcher("name", endsWith()) // <2>
+				.withIncludeNullValues() // <3>
+				.withIgnorePaths("role"); // <4>
+		Example<Employee> example = Example.of(employee, matcher); // <5>
+
+		Flux<Employee> employees = repository.findAll(example);
+
+		// do whatever with the flux
+		// end::example-2[]
+	}
+
+	@Data
+	@NoArgsConstructor
+	public class Employee {
+
+		private @Id Integer id;
+		private String name;
+		private String role;
+	}
+
+	public interface EmployeeRepository extends R2dbcRepository<Employee, Integer> {}
+}

Diff for: src/test/java/org/springframework/data/r2dbc/repository/ConvertingR2dbcRepositoryIntegrationTests.java

@@ -32,7 +32,6 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
-
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.annotation.ComponentScan;
 import org.springframework.context.annotation.Configuration;