Unable to store ManyToOne association for an entity

Question

I am unable to bind foreign_key baz_id to Baz on a POST call, it fails with a instantiation error trying to store a bar

POST http://localhost/foo/api/v1/bars
{
    "baz_id" : "1",
    "weight" : "1.0"

}

@NotNull
@ManyToOne
@JoinColumn(name = "baz_id", nullable = false, referencedColumnName = "id")
private Baz baz;

Answer 1

Your JSON is incorrect for the object being mapped. It should be of the form:

{
  "baz" : {"id":"1"},
  "weight" : "1.0"
}

this will allow Spring to build a bar instance that references a Baz instance with an id of 1.

Alternatively, if you use

{
  "baz_id" : "1",
  "weight" : "1.0"
}

your java entity will need to define a 'baz_id' property within it:

@Transient
private String baz_id;

Which your controller then uses to decide how to handle this value; ie using the appropriate findbyId method to set the baz reference before saving your Bar instance - this also gives you the opportunity to validate it does exist and decide what to do if it doesn't; create a new one or throw an appropriate exception.

Alternatively, you can map the String basic to the column, and only use that to set the value:

@ManyToOne
@JoinColumn(name = "baz_id", referencedColumnName = "id", insertable=false, updatable=false, fetch = FetchType.LAZY )
@JsonIgnore
private Baz baz;

@Column(name = "baz_id", nullable = false)
private String baz_id;

This will let you use the baz_id for REST api, but the baz reference for joins and other application usage.