java-crud-for-free-repositories-example-project

Java - databasing your code

NOTE:

• this project follows the Maven project structure (since it's pulling in libraries)
• so your Java files go in src/main/java/

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(1) Download copy of starter-project from Github

download an unZIP a copy of this started project from my public Github repositories

https://github.com/dr-matt-smith/java-crud-for-free-repositories-example-project

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(2) Update ".env" settings for your MySQL setup

edit the ".env" file to have your MySQL database credentials you can also change the name of the database to be created from movies20 to something else

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(3) locate the Main class and do a test run of this sample

Java source (.java files) code located in: /src/main/java/tudublin/

Build project (compile) with: mvn clean package

• if you have the PHP Composer tool you can just type composer build

Run your project with mvn exec:java

• note, the class congtaining the main() method to start your program's execution is declared in the <mainClass> element in the pom.xml Maven configuration file, which for this project is <mainClass>tudublin.Main</mainClass>

• if you have the PHP Composer tool you can just type composer go

you'll be editing this main class/script to create / store in DB / read and print your own objects ...

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(4) create "tudublin" package entity classes

(a) create / copy in your entity classes into the appropriate src folder

folder /src/main/java/tudublin/ package "tudublin"

(b) Note - my libraries don't yet work with enumerations so just delete any enumeration classes, and change enumeration types to strings for this database version of your code

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(5) create Repository classes for each of your entity classes

the library works by providing a powerful superclass offering DB CRUD methods

for each entity class

• add appropriate 'import' statement after the package/namespace statement
• for each entity create a class Repository that subclasses (extends) the Matt's 'magic' class: DatabaseTableRepository

import mattsmithdev.pdocrudrepo.DatabaseTableRepository;	

public class <MyEntity>Repository extends DatabaseTableRepository;	

e.g. for the Movie entity class we create a MovieRepository class as follows:

package tudublin;

import mattsmithdev.pdocrudrepo.DatabaseTableRepository;

public class MovieRepository extends DatabaseTableRepository
{
	// just inheritied methods for now
}

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(6) add an "int id" to every entity

the db-crud library requires every entity to have an integer id primary key property this allows the MySQL database to manage AUTO INCREMENTED primary keys for each database table row

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(7) for associated object properties change them to objectId properties (for foreign keys)

we have to manually convert object associations into foreign key "id" properties

(--a--) change object properties to "Id" properties

e.g. If the Movie entity is associated to a Directory entity with a "director" property in Movie we change this to "int directorId"

(--b--) add/generate get/set methods for the properties

e.g. for our Movie.directorId example: we add getDirectorId() and setDirectorId()

(--c--) delete any old set(...) method

e.g. for our Movie.directorId example: we delete method setDirector(...)

(--d--) replace the contents / create a getEntity() method for the associated object

we can use the related entity's Repository class, with the foreign key ID to retrieve the associated object

e.g. for our MMovie.directorId example: we replace the oldl getDirector() method with the following,using the foreign key ID

public Director getDirector()
{
DirectorRepository directorRepository = new DirectorRepository();
Director director = directorRepository.find(Directory.class, this.directorId);

return director;
}

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(8) for associated object properties update your (__)toString()

update the (__)toString() method for classes with associated object to make use of this.get()/$this->get() method

e.g. for the toString method for class Movie, with the directorId:

	... other toString() stuff here ...
	" director = " + this.getDirector()

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(9) create/update your Main.java to insert and then retrieve objects from the databasew

You can now create and use repository objects in your main class/script to store objects in the database and retrieve them

The general sequence is:

(--a--) create objects for each repositry class

(--b--) reset database tables with Repository.resetTable()/->resetTable()

(--c--) create all your objects for the entity classes

(--d--) insert the objects into the database with Repository.insert()/->insert()

(--e--) retreive an array of all objecss for each entity with = Repository.findAll()/->insert()

(--f--) use a for/foreach-loop to loop to print out each object via its toString

Examples:

    LecturerRepository lecturerRepository = new LecturerRepository();
    lecturerRepository.resetTable();

    Lecturer lecturer1 = new Lecturer();
    lecturer1.setName("matt");
    lecturerRepository.insert(lecturer1);

    Lecturer lecturer2 = new Lecturer();
    lecturer2.setName("jojo");
    lecturerRepository.insert(lecturer2);

    System.out.println("-- lecturers --");
    Lecturer[] lecturers = lecturerRepository.findAll(Lecturer.class);
    for (Lecturer lecturer : lecturers) {
        System.out.println(lecturer);
    }

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(10) you can add a helper method "createAndInsert(...)" in your repository class

personally, I like to create and insert it into the database all in one go (a bit like a constructor)

so I add methods like this to my repository classes, which create an object, set the properties and insert the object into the database

	package tudublin;

	import mattsmithdev.pdocrudrepo.DatabaseTableRepository;

	public class LecturerRepository extends DatabaseTableRepository
	{
	    public void createAndInsert(String name)
	    {
	        Lecturer lecturer = new Lecturer();
	        lecturer.setName(name);
	        this.insert(lecturer);
	    }
	}

So in our Main class we can create and insert a new object using the repository object all in one statement:

    lecturerRepository.createAndInsert("Jojo");