How to map Java/Kotlin string array and Postgres SQL array with JPA and hibernate

Question

I have a field in Postgres in array type:

 categories    | text[]         |           |          |

How can I declare the field in the entity class?

I have tried below in Product.kt file but it throws error [ERROR]:ERROR: relation "product_categories" does not exist

@ElementCollection
@Column(name = "categories")
var categories: List<String>? = emptyList()

My purpose is to save the string array as one field of the entity, I am not trying to do anything related "One to Many".

If you know any Java version solution and it works, I will accept the answer as well. Thanks

Answer 1

Adam's answer works for projects written in Java. As my project is written in Kotlin, I share my version below and hope it helps and people can use it right away other than spending time to convert:

Useful resource: How to map Java and SQL arrays with JPA and Hibernate

Postgres:

alter table product add column categories text[];

Gradle:

implementation("com.vladmihalcea:hibernate-types-52:2.10.0")

Product.kt

import com.vladmihalcea.hibernate.type.array.StringArrayType
import org.hibernate.annotations.*
import javax.persistence.*
import javax.persistence.Entity


@TypeDefs(
    TypeDef(name = "string-array", typeClass = StringArrayType::class)
)
@Entity
class Product(
        var name: String,

        @Type(type = "string-array")
        @Column(name = "categories", columnDefinition = "text[]")
        var categories: Array<String>? = arrayOf(),
)

There're 2 differences between Java and Kotlin:

1. The array type in Kotlin is Array<String> other than String[], I tried List<String> as well but it didn't work.
2. TypeDefs,TypeDef is different, no @ sign.

Answer 2

This won't work with @ElementCollection as it will always try to use another table. What you need is a custom type instead. For this you'll need this dependency:

<dependency>
    <groupId>com.vladmihalcea</groupId>
    <artifactId>hibernate-types-52</artifactId>
    <version>${hibernate-types.version}</version>
</dependency>

then you can define your own types:

import com.vladmihalcea.hibernate.type.array.StringArrayType

@TypeDefs({
    @TypeDef(
        name = "string-array", 
        typeClass = StringArrayType.class
    )
})
@Entity
class YourEntity {

    @Type( type = "string-array" )
    @Column(
        name = "categories", 
        columnDefinition = "character varying[]"
    )
    var categories: Array<String>;
}

I haven't tried this with a List though, as this maps to an Array. More info in this answer.