Feature/spring data mongodb skip and limit (#16285)

* mongo repo with @Aggregation in skip & limit

* add tests for skip & limit in MongoRepository

* cleanup

* fix spaces

* use BDD naming conventions

persistence-modules/spring-data-mongodb-2/src/main/java/com/baeldung/projection/model/Student.java

@@ -0,0 +1,36 @@
+package com.baeldung.projection.model;
+
+import org.springframework.data.annotation.Id;
+import org.springframework.data.mongodb.core.mapping.Document;
+
+@Document(collection = "student")
+public class Student {
+    @Id
+    private String id;
+    private String name;
+    private Long age;
+
+    public Student(String id, String name, Long age) {
+        this.id = id;
+        this.name = name;
+        this.age = age;
+    }
+    public String getId() {
+        return id;
+    }
+    public void setId(String id) {
+        this.id = id;
+    }
+    public String getName() {
+        return name;
+    }
+    public void setName(String name) {
+        this.name = name;
+    }
+    public Long getAge() {
+        return age;
+    }
+    public void setAge(Long age) {
+        this.age = age;
+    }
+}

persistence-modules/spring-data-mongodb-2/src/main/java/com/baeldung/projection/repository/StudentRepository.java

@@ -0,0 +1,32 @@
+package com.baeldung.projection.repository;
+
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.Pageable;
+import org.springframework.data.mongodb.repository.Aggregation;
+import org.springframework.data.mongodb.repository.MongoRepository;
+
+import com.baeldung.projection.model.Student;
+
+import java.util.List;
+
+public interface StudentRepository extends MongoRepository<Student, String> {
+    @Aggregation(pipeline = {
+      "{ '$skip': ?0 }",
+      "{ '$limit': ?1 }"
+    })
+    List<Student> findAll(Long skip, Long limit);
+    @Aggregation(pipeline = {
+      "{ '$match': { 'age': ?0 } }",
+      "{ $skip: ?1 }",
+      "{ $limit: ?2 }"
+    })
+    List<Student> findAllByAgeCriteria(Long age, Long skip, Long limit);
+    @Aggregation(pipeline = {
+      "{ '$match': { 'id' : ?0 } }",
+      "{ '$sort' : { 'id' : 1 } }",
+      "{ '$skip' : ?1 }",
+      "{ '$limit' : ?2 }"
+    })
+    List<Student> findByStudentId(final String studentId, Long skip, Long limit);
+    Page<Student> findAll(Pageable pageable);
+}

persistence-modules/spring-data-mongodb-2/src/test/java/com/baeldung/projection/StudentIntegrationTest.java

@@ -0,0 +1,90 @@
+package com.baeldung.projection;
+
+import com.baeldung.projection.config.ProjectionConfig;
+import com.baeldung.projection.model.Student;
+import com.baeldung.projection.repository.StudentRepository;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.PageRequest;
+import org.springframework.data.domain.Pageable;
+import org.springframework.data.domain.Sort;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration(classes = ProjectionConfig.class)
+public class StudentIntegrationTest {
+    @Autowired
+    private StudentRepository studentRepository;
+    private List<Student> studentList;
+
+    @Before
+    public void setUp() {
+        Student student1 = new Student("A", "Abraham", 15L);
+        Student student2 = new Student("B", "Usman", 30L);
+        Student student3 = new Student("C", "David", 20L);
+        Student student4 = new Student("D", "Tina", 45L);
+        Student student5 = new Student("E", "Maria", 33L);
+
+        studentList = Arrays.asList(student1, student2, student3, student4, student5);
+        studentRepository.saveAll(studentList);
+    }
+
+    @Test
+    public void whenRetrievingAllStudents_thenReturnsCorrectNumberOfRecords() {
+        // WHEN
+        List<Student> result = studentRepository.findAll(0L, 5L);
+        // THEN
+        assertEquals(5, result.size());
+    }
+
+    @Test
+    public void whenLimitingAndSkipping_thenReturnsLimitedStudents() {
+        // WHEN
+        List<Student> result = studentRepository.findAll(3L, 2L);
+        // THEN
+        assertEquals(2, result.size());
+        assertEquals("Tina", result.get(0).getName());
+        assertEquals("Maria", result.get(1).getName());
+    }
+
+    @Test
+    public void whenFilteringByAge_thenReturnsStudentsMatchingCriteria() {
+        // WHEN
+        List<Student> result = studentRepository.findAllByAgeCriteria(30L, 0L, 10L);
+        // THEN
+        assertEquals(1, result.size());
+        assertEquals("Usman", result.get(0).getName());
+    }
+
+    @Test
+    public void whenFindingById_thenReturnsMatchingStudent() {
+        // WHEN
+        List<Student> result = studentRepository.findByStudentId("A", 0L, 5L);
+        // THEN
+        assertEquals(1, result.size());
+        assertEquals("Abraham", result.get(0).getName());
+    }
+
+    @Test
+    public void whenFindByStudentIdUsingPageable_thenReturnsPageOfStudents() {
+        // GIVEN
+        Sort sort = Sort.by(Sort.Direction.DESC, "id");
+        Pageable pageable = PageRequest.of(0, 5, sort);
+
+        // WHEN
+        Page<Student> resultPage = studentRepository.findAll(pageable);
+
+        // THEN
+        assertEquals(5, resultPage.getTotalElements());
+        assertEquals("Maria", resultPage.getContent().get(0).getName());
+    }
+}