Spring Data MongoDB

Spring Data MongoDB is an Extremely useful tool for Java developers working with MongoDB databases. It simplifies data access and manipulation, provides a consistent programming model, and enhances developer productivity when building MongoDB-backed applications in the Spring ecosystem. It allows MongoDB collections and documents to be mapped to Java POJO classes using annotations like @Document and @Id. This object-document mapping reduces boilerplate code. It provides a MongoTemplate class for executing common MongoDB operations like find, save, update, and delete. This acts as the central API for data access.

Important Concepts in Spring Data MongoDB

• Repository: A repository is an interface that provides CRUD (create, read, update, delete) operations for a specific domain object. Spring Data MongoDB provides a number of repository interfaces that you can extend to get started quickly.
• Document: A document is a MongoDB data object. It is a JSON-like object that can be stored in a MongoDB collection.
• Query: A query is a way to retrieve documents from a MongoDB collection. Spring Data MongoDB provides a number of query methods that you can use to build queries.

To use Spring Data MongoDB, you need to

1. Install the Spring Data MongoDB dependency in your project.
2. Create a MongoDB database and collection.
3. Create a Spring Boot application.
4. Configure Spring Data MongoDB in your application.
5. Create a repository interface for your domain object.
6. Use the repository interface to store, retrieve, query, and manage data in MongoDB.

Working With Documents

• Define Java classes annotated with @Document to represent documents in MongoDB collections.
• The class name will be used as the collection name by default. Can specify collection name explicitly using @Document(collection=”collectionName”).
• Fields in the document are mapped to properties in the Java class. Use annotations like @Id, @Field, etc. to customize mapping.
• @Id annotation denotes the property that holds the unique identifier value of the document. It can be of any valid type like String, Integer, etc.

Relational Mapping

• Repositories provide a more declarative interface for data access compared to imperative MongoTemplate.
• Define a repository interface extending MongoRepository<EntityType, IdType> where EntityType is the document class and IdType is the id property type.
• This will provide implementations of common CRUD methods like save(), findById(), findAll() etc out of the box without writing any code.

MongoDB Query Language

• Query objects are used to build complex MongoDB queries programmatically.
• Create a Query instance and call methods like where(), regex(), etc. to add criteria.
• Common criteria methods are:
  • where(criteria) – add a Criteria object
  • regex(field, pattern) – regex match
  • near(point) – geospatial query
  • withinSphere(point, distance) – geospatial query
  • withinPolygon(polygon) – geospatial query

Example Project

Create a Spring Boot application and Install the Spring Data MongoDB dependency in your project:

1

XML

<?xml version="1.0" encoding="UTF-8"?>
<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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.1.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.mongo.demo</groupId>
    <artifactId>Spring_MongoDB</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>Spring_MongoDB</name>
    <description>Demo project for Spring Boot MongoDB</description>
    <properties>
        <java.version>17</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-mongodb</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

2

Create a MongoDB database and collection:

Configure Spring Data MongoDB in your application:

spring.data.mongodb.host=localhost
spring.data.mongodb.port=27017
spring.data.mongodb.database=Spring_MongoDB_Demo

Create a Pojo Class , Controller and repository interface for your project:

Java

// Pojo Class
package com.mongo.demo.entity;

import org.springframework.data.mongodb.core.mapping.Document;

@Document(collection = "employees")
public class Employee {
    private int id;
    private String emp_name;
    private String emp_city;
    private String emp_salary;

    public Employee()
    {
        super();
        // TODO Auto-generated constructor stub
    }

    public Employee(int id, String emp_name,
                    String emp_city, String emp_salary)
    {
        super();
        this.id = id;
        this.emp_name = emp_name;
        this.emp_city = emp_city;
        this.emp_salary = emp_salary;
    }

    public int getId() { return id; }

    public void setId(int id) { this.id = id; }

    public String getEmp_name() { return emp_name; }

    public void setEmp_name(String emp_name)
    {
        this.emp_name = emp_name;
    }

    public String getEmp_city() { return emp_city; }

    public void setEmp_city(String emp_city)
    {
        this.emp_city = emp_city;
    }

    public String getEmp_salary() { return emp_salary; }

    public void setEmp_salary(String emp_salary)
    {
        this.emp_salary = emp_salary;
    }
}

Java

// Controller
package com.mongo.demo.controller;

import com.mongo.demo.entity.Employee;
import com.mongo.demo.repository.EmployeeRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/employee")
public class EmployeeController {
    @Autowired
    private EmployeeRepository employeeRepository;

    @PostMapping("/")
    public ResponseEntity<?>
    addEmployee(@RequestBody Employee employee)
    {
        Employee save
            = this.employeeRepository.save(employee);
        return ResponseEntity.ok(save);
    }

    @GetMapping("/") public ResponseEntity<?> getEmployee()
    {
        return ResponseEntity.ok(
            this.employeeRepository.findAll());
    }
}

Java

// Employee Repository
package com.mongo.demo.repository;

import com.mongo.demo.entity.Employee;
import org.springframework.data.mongodb.repository.MongoRepository;

public interface EmployeeRepository
    extends MongoRepository<Employee, Integer> {
}

Output: