Why am I getting the \'Field required a bean of type that could not be found\' error in my Spring RESTful API with MongoDB?

'Field required a bean of type that could not be found' Error in Spring RESTful API Using MongoDB

When attempting to integrate MongoDB with a Spring RESTful API, users may encounter the error "'Field required a bean of type that could not be found.'" This error indicates that the Spring application is unable to locate an essential bean, in this case, the UserService bean.

The error arises from the way Spring scans for components in the project. By default, Spring scans for components within packages annotated with @SpringBootApplication. In this case, the UsersController class, which depends on the UserService, is located outside the default scan path.

To resolve this issue, there are two main approaches:

Approach 1: Customize Package Scanning

Manually specify the packages that should be scanned for components using the @SpringBootApplication(scanBasePackages={...}) annotation. In this case, add the following line to the main application class:

<code class="java">@SpringBootApplication(scanBasePackages={"main.java.service", "main.java.rest"})</code>

This will instruct Spring to scan both the service and rest packages for components.

Approach 2: Restructure Package Structure

Alternatively, restructure the project's package structure to ensure that all related components are within the same package. In this case, reorganize the project as follows:

src/
├── main/
│   └── java/
|       └── com.example/
|       |   ├── Application.java
|       |   ├── model/
|       |   |   └── User.java
|       |   ├── rest/
|       |   |   ├── IndexController.java
|       |   |   └── UsersController.java
|       |   ├── service/
|       |   |   └── UserService.java
└── resources/
    └── application.properties

This will ensure that all components related to the UserService are within the same package, and Spring will automatically scan them.

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