java - Spring Data Jpa and Specification - how to work with ManyToOne and ManyToMany relations? -

i have simple model in project.

[updatepackage] >- (manytoone) - [version] -< [usecase] - (manytomany)

public class updatepackage implements comparable<updatepackage> {      @manytoone(fetch = fetchtype.eager, cascade = cascadetype.all)     @joincolumn(name = column_orig_version, nullable = true)     private version origversion;  // setters , getters }  @entity @table(name = version.table_name) public class version {      @manytomany(fetch = fetchtype.eager, cascade = cascadetype.all)     @jointable(name = jvuc_table, joincolumns = { @joincolumn(name = jvuc_column_version, referencedcolumnname = column_id) }, inversejoincolumns = { @joincolumn(name = jvuc_column_usecase, referencedcolumnname = usecase.column_id) })     private final set<usecase> usecases = new hashset<usecase>();  // setters , getters }  @entity @table(name = usecase.table_name) public class usecase {      @column(name = column_name, nullable = false)     private string name;  // setters , getters } 

for implementation of filter use spring data jpa , specification spring.data.jpa.domain

for instance find list of updatepackage given usecase names.

i understand manytoone relation need use join , manytomany need use fetch.

my implementation of specification interface looks this:

public static specification<updatepackage> usecasenames(final list<string> usecasenames) {         return new specification<updatepackage>() {              @override             public predicate topredicate(root<updatepackage> root, criteriaquery<?> query,                     criteriabuilder cb) {                 final join<updatepackage, version> version = root.join(updatepackage_.destversion,                         jointype.left);                  fetch<version, usecase> usecase = version.fetch(version_.usecases, jointype.left);                 return null;                 // return usecase.get(usecase_.name).in(usecasenames);              }         };     } 

when run integration test got npexception in line:

fetch<version, usecase> usecase = version.fetch(version_.usecases, jointype.left); 

because fields joins , fetches of object version null.

i don't know in wrong way , cannot find answer in internet.

does know wrong in code?

stack: java.lang.nullpointerexception @ org.hibernate.ejb.criteria.path.abstractfromimpl.constructjoin(abstractfromimpl.java:261) @ org.hibernate.ejb.criteria.path.abstractfromimpl.fetch(abstractfromimpl.java:549)

i've found solution. had bug in static model.

static model from:

public static volatile singularattribute<version, usecase> usecases; 

to:

public static volatile setattribute<version, usecase> usecases; 

and in implementation of specification:

public static specification<updatepackage> usecasenames(final list<string> usecasenames) {         return new specification<updatepackage>() {              @override             public predicate topredicate(root<updatepackage> root, criteriaquery<?> query,                     criteriabuilder cb) {                                final join<updatepackage, version> version = root.join(updatepackage_.destversion,                         jointype.left);                 final join<version, usecase> usecase = version.join(version_.usecases);                 return usecase.get(usecase_.name).in(usecasenames);             }         };     }