Adding a Car Class
One-To-Many Relation
Clarifications
At the end of the video, the person
column in the car table (the table to the right) is called a foreign key column as the values in the column are ids on the person table (table to the left)
One-To-Many Implementation
Clarification
Car Controller
The annotation @Controller
was mistakenly used instead of @RestController
in class CarController
. @RestController
is a newer annotation that removes the need of using a @ResponseBody
annotation to wrap the return type in a response class. However, if you are returning the type ResponseEntity<T>
it shouldn't make a difference.
CascadeType
When using a one-to-many relationship it is often relevant to set a cascade type. This decides which actions on an entity should be propagated to its collection of another entity. In our case, if we want the cars to be deleted when the person who owns them gets deleted we should set a value on the @ManyToOne
annotation cascade = CascadeType.ALL
for all actions (including deletion, persisting) to affect the cars. If you only want deletion specifically to be propagated then you would set the value to cascade = CascadeType.REMOVE
. See Overview of JPA/Hibernate Cascade Types
Avoiding Recursive JSON Representation
Snippets & Commands
JSON annotations
Ignore the property completely:
@JsonIgnore
or make the property only be rendered as the id:
@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
@JsonIdentityReference(alwaysAsId = true)
Updating Car & Validation
Clarifications
Car Field Validation
At the very end of the video. The field topSpeed
is annotated with @NotBlank
but that annotation actually doesn't work on int
fields because compared to a String
, an int
has no concept of being empty (int value 0 is not considered empty) so there you would have to use @NotNull
instead.
Validation Groups
If you would like to validate an object differently depending on which method it is used (for example in one controller method you might want to enforce a non-null reference to another entity but in another you want the reference to be able to be omitted) you can use Validation Groups, see this link.
Snippets & Commands
build.gradle
plugins {
id 'org.springframework.boot' version '2.4.4'
id 'io.spring.dependency-management' version '1.0.11.RELEASE'
id 'java'
}
repositories {
mavenCentral()
}
dependencies {
implementation 'org.springframework.boot:spring-boot-starter-web'
implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
implementation 'org.springframework.boot:spring-boot-starter-validation'
runtimeOnly 'org.postgresql:postgresql'
}
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