Creating an entity
Please check our video tutorial on creating a new JHipster application!
Introduction
Once you have created your application, you will want to create entities. For example, you might want to create an Author and a Book entity. For each entity, you will need:
- A database table
- A Liquibase change set
- A JPA Entity
- A Spring Data JPA Repository
- A Spring MVC REST Controller, which has the basic CRUD operations
- An AngularJS router, a controller and a service
- An HTML view
- Integration tests, to validate everything works as expected
- Performance tests, to see if everything works smoothly
If you have several entities, you will likely want to have relationships between them. For this, you will need:
- A database foreign key
- Specific JavaScript and HTML code for managing this relationship
The “entity” sub-generator will create all the necessary files, and provide a CRUD front-end for each entity (see project structure). The sub generator can be invoked by running yo jhipster:entity <entityName> --[options]
. Reference for those options can be found by typing yo jhipster:entity --help
Below are the supported options.
--table-name <table_name>
- By default JHipster will generate a table name based on your entity name, if you would like to have a different table name you can do so by passing this option.--angular-suffix <suffix>
- If you want all your AngularJS routes to have a custom suffix you can pass that using this option.--regenerate
- This will regenerate an existing entity without asking any questions.--skip-server
- This will skip the server-side code and will generate only the client-side code.--skip-client
- This will skip the client-side code and will generate only the server-side code.
JHipster UML and JDL Studio
This page describes how to create entities with JHipster using the standard command-line interface. If you want to create many entities, you might prefer to use a graphical tool.
In that case, two options are available:
- JHipster UML, which allows you to use an UML editor.
- JDL Studio, our online tool to create entities and relationships using our domain-specific language JDL.
If you used the JDL Studio:
- You can generate entities from a JDL file using the
import-jdl
sub-generator, by runningyo jhipster:import-jdl your-jdl-file.jh
. - If you want to use JHipster UML instead of the
import-jdl
sub-generator, you need to install it by runningnpm install -g jhipster-uml
, and then runjhipster-uml yourFileName.jh
.
Entity fields
For each entity, you can add as many fields as you want. You will need to input the field names and their types, and JHipster will generate for you all the required code and configuration, from the AngularJS HTML view to the Liquibase changelog.
Those fields cannot contain reserved keywords in the technologies you are using. For example, if you use MySQL:
- You cannot use Java reserved keywords (as your code will not compile)
- You cannot use MySQL reserved keywords (as your database schema update will fail)
Field types
JHipster supports many field types. This support depends on your database backend, so we use Java types to describe them: a Java String
will be stored differently in Oracle or Cassandra, and it is one of JHipster’s strengths to generate the correct database access code for you.
String
: A Java String. Its default size depends on the underlying backend (if you use JPA, it’s 255 by default), but you can change it using the validation rules (putting amax
size of 1024, for example).Integer
: A Java Integer.Long
: A Java Long.Float
: A Java Float.Double
: A Java Double.BigDecimal
: Ajava.math.BigDecimal
object, used when you want exact mathematic calculations (often used for financial operations).LocalDate
: Ajava.time.LocalDate
object, used to correctly manage dates in Java.ZonedDateTime
: Ajava.time.ZonedDateTime
object, used to correctly manage dates and times in Java.Boolean
: A Java Boolean.enum
: A Java Enumeration object. When this type is selected, the sub-generator will ask you what values you want in your enumeration, and it will create a specificenum
class to store them.byte[]
: A Blob object, used to store some binary data. When this type is selected, the sub-generator will ask you if you want to store some generic binary data, or an image object. Images will be handled specifically on the AngularJS side, so they can be displayed to the end-user.
Validation
Validation can be set up for each field. Depending on the field type, different validation options will be available.
Validation will be automatically generated on:
- the HTML views, using the AngularJS validation mechanism
- the Java domain objects, using Bean Validation
Bean validation will then be used to automatically validate domain objects when they are used in:
- Spring MVC REST controllers (using the
@Valid
annotation) - Hibernate/JPA (entities are automatically validated before being saved)
Validation information will also be used to generate more precise database column metadata:
- Required fields will be marked non-nullable
- Fields which have a maximum length will have the same column length
Validation has a few limitations:
- We don’t support all validation options from AngularJS and Bean Validation, as we only support those which are common to both APIs
- Regular Expression patterns don’t work the same in JavaScript and in Java, so if you configure one, you might need to tweak one of the generated patterns
- JHipster generates unit tests that work for generic entities, without knowing your validation rules: it is possible that the generated tests do not pass the validation rules. In that case, you will need to update the sample values used in your unit tests, so that they pass the validation rules.
Entity relationships
Entity relationships are only available for SQL databases. It is a fairly complex subject, which has its own documentation page: Managing relationships.
Data Transfer Objects (DTOs)
By default JHipster entities do not use DTOs, but they are available as an option. Here is the documentation: Using DTOs.
Pagination
Please note that pagination is not available if you created your application with Cassandra. Of course this will be added in a future release.
Pagination uses the Link header, as in the GitHub API. JHipster provides a custom implementation of this specification on both the server (Spring MVC REST) and client (AngularJS) sides.
When the entity is generated, JHipster provides 4 pagination options:
- No pagination (in that case, the back-end won’t be paginated)
- A simple pager, based on the Bootstrap pager
- A complete pagination system, based on the Bootstrap pagination component
- An infinite scroll system, based on the infinite scroll directive
Updating an existing entity
The entity configuration is saved in a specific .json
file, in the .jhipster
directory. So if you run the sub-generator again, using an existing entity name, you can update or regenerate the entity.
When you run the entity sub-generator for an existing entity, you will be asked a question ‘Do you want to update the entity? This will replace the existing files for this entity, all your custom code will be overwritten’ with following options:
Yes, re generate the entity
- This will just regenerate your entity. Tip: This can be forced by passing a--regenerate
flag when running the sub-generatorYes, add more fields and relationships
- This will give you questions to add more fields and relationshipsYes, remove fields and relationships
- This will give you questions to remove existing fields and relationships from the entityNo, exit
- This will exist the sub-generator without changing anything
You might want to update your entity for the following reasons:
- You want to add/remove fields and relationships to an existing entity
- You want to reset your entity code to its original state
- You have updated JHipster, and would like to have your entity generated with the new templates
- You have modified the
.json
configuration file (the format is quite close to the questions asked by the generator, so it’s not very complicated), so you can have a new version of your entity - You have copy/pasted the
.json
file, and want a new entity that is very close to the copied entity
TIP: to regenerate all your entities at once, you can use the following commands (remove the --force
to have questions asked when files have changed).
- Linux & Mac:
for f in `ls .jhipster`; do yo jhipster:entity ${f%.*} --force ; done
- Windows:
for %f in (.jhipster/*) do yo jhipster:entity %f --force
Tutorial
This is a short tutorial on creating two entities (a Author and a Book) which have a one-to-many relationship.
Generate the “Author” entity
As we want to have a one-to-many relationship between Authors and Books (one author can write many books), we need to create the Author first. At the database level, JHipster will then be able to add a foreign key on the Book table, linking to the Author table.
yo jhipster:entity author
Answer the next questions concerning the fields of this entity, the author has:
- a “name” of type “String”
- a “birthDate” of type “LocalDate”
Then answer the questions concerning the relationships, the author has:
- A one-to-many relationship with the “book” entity (which doesn’t exist yet)
Generate the “Book” entity
yo jhipster:entity book
Answer the next questions concerning the fields of this entity, the book has:
- a “title”, of type “String”
- a “description”, of type “String”
- a “publicationDate”, of type “LocalDate”
- a “price”, of type “BigDecimal”
Then answer the questions concerning the relationships, the book:
- Has many-to-one relationship with the “author” entity
- And this relationship uses the “name” field (from the Author entity) to be displayed
Check the generated code
Run the generated test suite, with mvn test
, which will test the Author entity and the Book entity.
Launch the application (for example with mvn
), log in and select the “Author” and “Book” entities in the “entities” menu.
Check the database tables, to see if your data is correctly inserted.
Improve the generated code
The generated files contain all the basic CRUD operations, and don’t need to be modified if your needs are simple.
If you want to modify the generated code or the database schema, you should follow our development guide
If you want some more complex business behaviors, you might need to add a Spring @Service
class, using the service sub-generator.
You’re done!
Your generated CRUD page should look like this: