Hibernate associations

The following post is for playing with the assiocations.

Uni-directional

 public class SourceEntity {

@Id

private Long id;

private String name;

@OneToMany

private List<TargetEntity> targets;

}

public class TargetEntity {

@Id

private Long id;

private String description;

}

Both tables have two columns each. No FK column is added.

For the able table, the third table is "source_entity_targets" is created with two columns "source_entity_id" and "target_id".

Bi-directional

If I add convert it to bi-directional, still it will create a third table. Following changes are added for bi-directional and Target Entity looks like. 

public class TargetEntity {

@Id

private Long id;

private String description;

@ManyToOne(fetch = FetchType.LAZY)

    private SourceEntity sourceEntity;

}

This time the target entity table has "source_entity_id" column as well. It is "MUL" key.

Adding @JoinColumn annotation in Source table

public class SourceEntity {

@Id

private Long id;

private String name;

        @OneToMany(cascade = {CascadeType.ALL})

@JoinColumn

private List<TargetEntity> targets;

}

public class TargetEntity {

@Id

private Long id;

private String description;

@ManyToOne(fetch = FetchType.LAZY)

private SourceEntity sourceEntity;

}

This creates two tables. The source table has 2 columns, Target tables have 4 columns out of which 2 columns are: source_entity_id and targets_id. 

On saving the object, the source_entity id was saved in target_ids.

Join Column name

When I added the name to the Join column annotation as following in the source entity class.

Two tables were created.

@OneToMany(cascade = {CascadeType.ALL})

@JoinColumn(name="source_id")

private List<TargetEntity> targets;

Target table's column name "targets_id" is converted to "source_id".

When I added the @JoinColumn annotation in targetClass as 

@ManyToOne(fetch = FetchType.LAZY)

@JoinColumn(name="source_id")

private SourceEntity sourceEntity;

Three tables were created.

source_entity has 2 columns.

The target entity has now 3 columns. The third column is "source_id".

And source_entity_targets table with two columns as discussed above.

When saved an object, the source_id was set to null and the source_entity_targets columns had values.

After adding the following to source

@OneToMany(cascade = {CascadeType.ALL}, mappedBy = "sourceEntity") 

private List<TargetEntity> targets;

2 tables were created but the source id was not saved in the target table. the source_id column value was set to null.

To fix this, a new sourceEntity should be added to the target entity before saving the source entity. Example: 

SourceEntity src = new SourceEntity();

src.setName("source");

List<TargetEntity> targetEntities = new ArrayList<>();

TargetEntity target = new TargetEntity();

target.setDescription("description");

target.setSourceEntity(src); // <<<<< this line adds the source to target.

targetEntities.add(target);

src.setTargets(targetEntities);

dataService.persistData(src);

Junit - Parameterized Unit Testing - CsvFileSource

Sometimes we need to execute a single test case multiple times.

In Java, For this purpose using JUnit's Parameterized testing is a good approach. 

It allows us to provide test data in an iterable format and code runs for all the records. In this series, I will try to cover different ways of providing iterable data to unit tests. 

In this tutorial, we will read the data from a CSV file with the annotation @CsvFileSource. It will use a comma-separated file as an input data source.

In Junit, We use the @Test annotation to mark a method as a test case. In case of making a test Parameterized, We need to add the annotation `@ParameterizedTest` instead of @Test and mention the input file as a parameter in `@CsvFileSource`.

@ParameterizedTest

 @CsvFileSource(resources = "/input_test_data.csv", numLinesToSkip = 1)

You can see another parameter named 'numLinesToSkip' which is used to skip these lines for the testing. In this case, I have added 1 to skip the header name.

To start the example, First, create a CSV file under the directory 'src/test/resources' and name it whatever you want. For this example, the file name is "input_test_data" with two columns. i.e. First Name and Last Name. Following are the contents of our CSV file.

First Name, Last Name

Ragnar, Lothbrok

Now create a Java class in the test folder and put the following contents in the file.\

import org.junit.jupiter.params.ParameterizedTest;

import org.junit.jupiter.params.provider.CsvFileSource;

class ParameterizedUnitTest {

    @ParameterizedTest

    @CsvFileSource(resources = "/input_test_data.csv", numLinesToSkip = 1)

public void testCategories(String firstName, String lastName) {

System.out.print("Full Name is :"+firstName+" "+lastName);

}

}

Now you can run the test by adding multiple records to your CSV file.

Happy coding.