In this chapter, we are going to learn how to make CRUD operation using JPA repository.\u00a0 As mentioned before, the repository provides methods to perform these operations.The only file we need to modify is the StudentService file.<\/p>\n
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Let’s open the StudentRepository and make a little change. We should actually have done this in the previous chapter. The modified class is shown below.<\/p>\n
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package<\/span> com.<\/span>kindsonthegenius<\/span>.<\/span>social<\/span>.<\/span>student<\/span>;<\/span>\r\n\r\nimport<\/span> org.springframework.data.repository.CrudRepository<\/span>;<\/span>\r\n\r\npublic<\/span> interface<\/span> StudentRepository<\/span> extends<\/span> CrudRepository<<\/span>Student,<\/span> String><\/span> {<\/span>\r\n\r\n}<\/span>\r\n<\/pre>\n <\/p>\n
Note the we have provided the Student and String.The Student is the entity type while the String is the primary key type.<\/p>\n
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2. AutoWire the Repository into the Service<\/strong><\/h4>\nThe very first step is to AutoWire the StudentRepository into the Student Service. So open the StudenRepository class. Create a private member variable of StudentReposiory. Then add @Autowired to this variable. If you do this, the StudentService class would be as shown below:<\/p>\n
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package<\/span> com.<\/span>kindsonthegenius<\/span>.<\/span>social<\/span>.<\/span>student<\/span>;<\/span>\r\n\r\nimport<\/span> org.springframework.beans.factory.annotation.Autowired<\/span>;<\/span>\r\nimport<\/span> org.springframework.stereotype.Service<\/span>;<\/span>\r\n\r\n@Service<\/span>\r\npublic<\/span> class<\/span> StudentService<\/span> {<\/span>\r\n\t\r\n\t@Autowired<\/span>\r\n\tpublic<\/span> StudentRepository studentRepository;<\/span>\r\n\t\r\n \/\/ The Crud methods goes here<\/span>\r\n}<\/span>\r\n<\/pre>\n <\/p>\n
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3. Get List of Students<\/strong><\/h4>\nFirst, we get a list of Students. To do that we use the findAll()<\/strong> method.So this means that we can use a single line as shown below to get all records.<\/p>\n <\/p>\n
studentRepository.findAll<\/span>();\r\n<\/pre>\n <\/p>\n
This one line is all is needed to connect to do the following:<\/p>\n
\n- connect to the database<\/li>\n
- run a query to get all the Student records<\/li>\n
- convert each of the returned rows to Student instances<\/li>\n
- return it back to the service<\/li>\n<\/ul>\n
The findAll() method returns an iterable. So we need to convert it into a list. The complete code is given below:<\/p>\n
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public<\/span> List<<\/span>Student><\/span> getAllStudents<\/span>()<\/span> {<\/span>\r\n\t\r\n List<<\/span>Student><\/span> students =<\/span> new<\/span> ArrayList<>();<\/span>\r\n\t\r\n studentRepository.<\/span>findAll<\/span>()<\/span>\r\n .<\/span>forEach<\/span>(<\/span>students:<\/span>:<\/span>add);<\/span>\r\n\t\r\n return<\/span> students;<\/span>\t\t\r\n}<\/span>\r\n<\/pre>\n <\/p>\n
What we do here is that we created an empty list of Student. Then we iterate through the list returned by findAll(). For each item in the list, we add it to the students list we created. We have used a method reference here (::). We could actually test this method now. However, we’ve not populated our controller class. Besides, there is nothing in the database. So we would have an empty result. So the next thing to do is to add a method to add new Student.<\/p>\n
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4. Add a Student<\/strong><\/h4>\nTo add a new Student is really easy. You do this by using the StudentRepository save()<\/strong><\/em> method. You simply pass it as parameter, the Student instance you want to save.<\/p>\nThe method is given below.<\/p>\n
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public<\/span> void<\/span> addStudent<\/span>(<\/span>Student student)<\/span> {<\/span>\r\n studentRepository.<\/span>save<\/span>(<\/span>student);<\/span>\r\n}<\/span>\r\n<\/pre>\n <\/p>\n
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5. Get Student by Id<\/strong><\/h4>\nAgain, the StudentRepository provides a method findById(). This methods takes the id of the Student to find. This method use to be findOne(). But since Spring data jpa 2.0 it’s changed to findById(). Also note the Optional keword. This is there to prevent nullPointerException in case the record is not found.<\/p>\n
The code snipped is given below:<\/p>\n
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public<\/span> Optional<<\/span>Student><\/span> getStudent<\/span>(<\/span>String id)<\/span> {<\/span>\r\n return<\/span> studentRepository.<\/span>findById<\/span>(<\/span>id);<\/span>\r\n}<\/span>\r\n<\/pre>\n <\/p>\n
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6. Update a Student<\/strong><\/h4>\nTo update a Student record, we used the same save() method as with adding a new Student.<\/p>\n
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public<\/span> void<\/span> updateStudent<\/span>(<\/span>String id, Student student)<\/span> {<\/span>\r\n studentRepository.<\/span>save<\/span>(<\/span>student);<\/span>\r\n}<\/span>\r\n<\/pre>\n <\/p>\n
This is what happens with update: if the record exists, then it is updates. If however, the record with the id does not exist, then it adds a new record.<\/p>\n
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7. Delete a Student<\/strong><\/h4>\nTo delete a Student record, you simply use the deleteById() method provided by the StudentRepository. The you pass in the id of the record you want to delete.<\/p>\n
The code is given below:<\/p>\n
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public<\/span> void<\/span> deleteStudent<\/span>(<\/span>String id)<\/span> {<\/span>\r\n studentRepository.<\/span>deleteById<\/span>(<\/span>id);<\/span>\r\n}<\/span>\r\n<\/pre>\n <\/p>\n
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8. Build the Controller Class<\/strong><\/h4>\nNow we are going to write out controller methods in the controller class. It is fairly easy. It’s exacly similar to the other controllers we’ve written. So I would just provide you with the code as shown below:<\/p>\n
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@RestController<\/span>\r\npublic<\/span> class<\/span> StudentController<\/span> {<\/span>\r\n\t\r\n\t@Autowired<\/span>\r\n\tprivate<\/span> StudentService studentService;<\/span>\r\n\r\n\t @RequestMapping<\/span>(<\/span>value =<\/span> \"\/students\"<\/span>)<\/span>\r\n\t public<\/span> List<<\/span>Student><\/span> getAllStudents<\/span>()<\/span> \r\n\t {<\/span>\t\t\r\n\t\treturn<\/span> studentService.<\/span>getAllStudents<\/span>();<\/span>\r\n\t }<\/span>\t\r\n\t \r\n\t \r\n\t @RequestMapping<\/span>(<\/span>value =<\/span> \"\/students\/{id}\"<\/span>)<\/span>\r\n\t public<\/span> Optional<<\/span>Student><\/span> getStudent<\/span>(<\/span>@PathVariable<\/span> String id)<\/span> {<\/span>\r\n\t \treturn<\/span> studentService.<\/span>getStudent<\/span>(<\/span>id);<\/span>\r\n\t }<\/span>\r\n\t \r\n\t \r\n\t @RequestMapping<\/span>(<\/span>value =<\/span> \"\/students\"<\/span>,<\/span> method=<\/span>RequestMethod.<\/span>POST<\/span>)<\/span>\r\n\t public<\/span> void<\/span> addStudent<\/span>(<\/span>@RequestBody<\/span> Student student)<\/span> {<\/span>\r\n\t\t studentService.<\/span>addStudent<\/span>(<\/span>student);<\/span>\r\n\t }<\/span>\r\n\t \r\n\t @RequestMapping<\/span>(<\/span>value =<\/span> \"\/students\/{id}\"<\/span>,<\/span> method =<\/span> RequestMethod.<\/span>PUT<\/span>)<\/span>\r\n\t public<\/span> void<\/span> updateStudent<\/span>(<\/span>@RequestBody<\/span> Student student,<\/span>@PathVariable<\/span> String id )<\/span> {<\/span>\r\n\t\t studentService.<\/span>updateStudent<\/span>(<\/span>id,<\/span> student);<\/span>\r\n\t }<\/span>\r\n\t \r\n\t @RequestMapping<\/span>