Spring Data JPA Specification search for property in nested collection

Say I have at least two entities.

@Entity
public class Process {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(unique = true)
private String name;
@ManyToAny(
metaColumn = @Column(name = "node_type"),
fetch = FetchType.LAZY
)
@AnyMetaDef(
idType = "long", metaType = "string",
metaValues = {
@MetaValue(targetEntity = Milestone.class, value = MILESTONE_DISC),
@MetaValue(targetEntity = Phase.class, value = PHASE_DISC)
}
)
@Cascade({org.hibernate.annotations.CascadeType.ALL})
@JoinTable(
name = "process_nodes",
joinColumns = @JoinColumn(name = "process_id", nullable = false),
inverseJoinColumns = @JoinColumn(name = "node_id", nullable = false)
)
private Collection<ProcessNode> nodes = new ArrayList<>();
...
}

@Entity
@ToString
@DiscriminatorValue(MILESTONE_DISC)
public class Milestone implements ProcessNode {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
private Collection<ResultDefinition> results;
@ToString.Exclude
@ManyToOne(fetch = FetchType.LAZY)
@Transient
private Process process;
...
}

Now I want to use spring data jpa specification to find (all) processes which have a milestone with name "S5".

Note that Milestone is a ProcessNode and there is another Entity called Phase which is also a ProcessNode. These can be contained in the "nodes" collection of my Process Entity.

I tried to write something like this:

    public static Specification<Process> hasMilestoneWithName(final String milestoneName) {
return (Specification<Process>) (root, query, criteriaBuilder) -> {
Path<?> namePath = root.join("nodes").get("name");
return criteriaBuilder.equal(namePath, milestoneName);
};
}

This does not work, but throws:

> Caused by: java.lang.IllegalArgumentException: Unable to locate Attribute with the the given name [nodes] on this ManagedType [com.smatrics.dffs.processservice.model.entities.Process]

I don't really know how to use the API. Examples often refer to a meta-model that would be generated by the IDE or maven, but I really do not want to have any static generated resources. Please help me resolve this with Specification of spring-data-jpa without a generated meta-model.

Also if you could help me write the hql it would be awesome.

Thanks!

I would suggest a simpler alternative, coming from bottom-up:

• Load Milestone entities with name=S5: findByName("S5")
• Return the Process for each Milestone
• Filter out the duplicates

Or you could even save a few SQL queries by returning not the Milestone entity but only the ID of the Process for each Milestone and then load the Process nodes by a list of IDs:

The (native) SQL equivalent would be

select *
from process
where id in (
select process_id
from milestone
where name = 'S5'
)

Regardless of my solution your join does not look completely correct to me but I can't point out what's wrong - maybe there are other methods on the JPA metamodel that return a CollectionJoin? Not sure. Probably it is because @ManyToAny is not JPA standard so the JPA criteria API does not recognize nodes as a valid "joinable" field.