This is a Spring Boot + MongoDB comparison between Querydsl and MongoTemplate:

• Querydsl
• MongoTemplate

Prerequisites

A MongoDB or Docker to run it from an image, Maven

Start the application

If you don't have a MongoDB running, the app work well with a Docker container:

docker run --name mymongo -d mongo:jessie

Once started, the application will create a database called "data" and a collection called bestPracticesDocument containing 10 records.

To compile and start the app (Uses port 8090 and try to connect to MongoDB on the default port (27017):

mvn spring-boot:run

API

Once started you can try the api using curl or Postman as following (Querydsl):

localhost:8090/api/v1/bestpractices/documents/?description=bp

localhost:8090/api/v1/bestpractices/documents/?description=bp&phase=6

localhost:8090/api/v1/bestpractices/documents/?description=bp&phase=bp&size=3&page=2

Or that version with (MongoTemplate):

localhost:8090/api/v1/bestpractices/documents/search?description=bp
localhost:8090/api/v1/bestpractices/documents/search?description=bp&phase=6
localhost:8090/api/v1/bestpractices/documents/search?description=bp&phase=bp&size=3&page=2
localhost:8090/api/v1/bestpractices/documents/search?categories=cat0

Implementation Details (Querydsl)

The following maven plugin is generating Query type objects from the @Document entity:

				<groupId>com.mysema.maven</groupId>
				<artifactId>apt-maven-plugin</artifactId>
				<version>${apt.version}</version>
				<dependencies>
					<dependency>
						<groupId>com.querydsl</groupId>
						<artifactId>querydsl-apt</artifactId>
						<version>${querydsl.version}</version>
					</dependency>
				</dependencies>
				<executions>
					<execution>
						<phase>generate-sources</phase>
						<goals>
							<goal>process</goal>
						</goals>
						<configuration>
							<outputDirectory>src/main/java/generated-sources/queries</outputDirectory>
							<processor>org.springframework.data.mongodb.repository.support.MongoAnnotationProcessor</processor>
							<logOnlyOnError>true</logOnlyOnError>
						</configuration>
					</execution>
				</executions>
			</plugin>

The repository interface extends from QuerydslPredicateExecutor which is typed with the "Query type" object that was generated by the MongoAnnotationProcessor (see above). When a REST call is done the MongoDB implementation of QuerydslPredicateExecutor : QuerydslMongoPredicateExecutor is using the generated Predicate from the request to query the DB.

The repository interface:

public interface BestPracticesRepository
        extends CrudRepository<BestPracticesDocument, String>, QuerydslPredicateExecutor<BestPracticesDocument>, QuerydslBinderCustomizer<com.example.pocQuerydsl.BestPractices.QBestPracticesDocument> {

    /*
     * (non-Javadoc)
     * @see org.springframework.data.querydsl.binding.QuerydslBinderCustomizer#customize(org.springframework.data.querydsl.binding.QuerydslBindings, com.mysema.query.types.EntityPath)
     */
    @Override
    default public void customize(QuerydslBindings bindings, com.example.pocQuerydsl.BestPractices.QBestPracticesDocument doc) {

        bindings.bind(String.class).first((StringPath path, String value) -> path.containsIgnoreCase(value));
        //bindings.excluding(doc.id);
    }
}

The REST controller:

 @GetMapping(value = "/documents", produces = MediaType.APPLICATION_JSON_VALUE)
    public ResponseEntity<List<BestPracticesDocument>> getDocument(@QuerydslPredicate(root = BestPracticesDocument.class) Predicate predicate, //
                                                                   @PageableDefault(sort = { "description", "phase" }) Pageable pageable, //
                                                                   @RequestParam MultiValueMap<String, String> parameters){
        return new ResponseEntity<>(repository.findAll(predicate, pageable).stream().collect(Collectors.toList()), HttpStatus.OK);
    }