Avoiding two distinct domain models with Spring Boot and Jackson - json

Question

I'm designing a Spring Boot REST API that will be backed by MySQL. It has occurred to me that I want, effectively, two separate models for all my domain objects:
Model 1: Used between the outside world (REST clients) and my Spring REST controllers; and
Model 2: The entities used internally between by Spring Boot app and the MySQL database
For instance I might have a contacts table for holding personal/contact info:
CREATE TABLE contacts (
contact_id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
contact_ref_id VARCHAR(36) NOT NULL,
contact_first_name VARCHAR(100) NOT NULL,
...many more fields
);
and the respective Spring/JPA/Hibernate entity for it might look like:
// Groovy pseudo-code!
#Entity
class Contact {
#Id
#Column(name = "contact_id")
#GeneratedValue(strategy = GenerationType.IDENTITY)
Long id
#Column(name = "contact_ref_id")
UUID refId
#Column(name = "contact_first_name")
String firstName
// ...etc.
}
If I only had a single model paradigm, then when Jackson goes to serialize a Contact instance (perhaps fetched back from the DB) into JSON and send it back to the client, they'd see JSON that looks like:
{
"id" : 45,
"refId" : "067e6162-3b6f-4ae2-a171-2470b63dff00",
"firstName" : "smeeb",
...
}
Nothing like exposing primary keys to the outside world! Instead, I'd like the serialized JSON to omit the id field (as well as others). Another example might be a lookup/reference table like Colors:
# Perhaps has 7 different color records for ROYGBIV
CREATE TABLE colors (
color_id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
color_name VARCHAR(20) NOT NULL,
color_label VARCHAR(20) NOT NULL,
color_hexcode VARCHAR(20) NOT NULL,
# other stuff here
);
If the corresponding Color entity looked like this:
#Entity
class Color {
#Id
#Column(name = "color_id")
#GeneratedValue(strategy = GenerationType.IDENTITY)
Long id
#Column(name = "color_name")
String name
#Column(name = "color_label")
String label
#Column(name = "color_hexcode")
String hexcode
// ...etc.
}
Then with only one model it would serialize into JSON like so:
{
"id" : 958,
"name" : "Red",
"label" : "RED",
"hexcode" : "ff0000"
}
But maybe I just want it to come back as a simple string value:
{
"color" : "RED"
}
So it seems to me that I either need two separate models (and mapper classes that map between them) or I need a way to annotate my entities or configure either Spring, Jackson or maybe even Hibernate to apply certain transformations on my entities at the right time. Do these frameworks offer anything that can help me here, or am I going to have to go with two distinct domain models here?

Answer 1

You can actually accomplish this with just one model and I think it is the easiest way if you are just looking for hiding fields, custom formatting, simple transformation of attributes etc. Having two models require transformation from one model to another and vice-versa which is a pain. Jackson provides a lot of useful annotations which can be used to customize the output. Some of the annotations that can be useful for you are listed below
#JsonIgnore - ignore a field/attribute. You can hide your id field using this annotation.
#JsonInclude - Can be used to specify when a field should be present in output. For eg: Whether a field should be present in output if it is null
#JsonSerialize - You can specify a custom serializer for an attribute. For eg: You have an attribute 'password' and you want to output password as '****'.
#JsonFormat - You can apply a custom format to a field. This is very useful if you have date/time fields
#JsonProperty - If you want to give a different name for your field in your output. For eg: You have a field 'name' in your model and you want to display it as 'userName' in the output.