Query Many-to-many jpa - sql

Question

I need to implement SELECT with a many-to-many relationship in #QUERY. Perhaps I am misinterpreting the information written in the documentation.
My query looks like this:
#Query("select massages.id from massages join string_massage on massages.id = string_massage.massage_id where string_massage.string_id = ?1")
List<MasageEntity> findMassagesIdByStringId(#Param("strings_id") long strings_id);
In my example, I use table names. The names are underlined as an error (without compilation). Maybe I should use Entities. Then how do I do it with many-to-many relationship?
I will show a part of my Entities.
I have two Entities. MasageEntity and RstringEntity.
//MasageEntity
#Entity
#Table(name = "massages")
public class MasageEntity {
#Id
#GeneratedValue (strategy = GenerationType.IDENTITY)
private Long id;
#Column(name = "string_text")
private String string_text;
#Column(name = "string_speed")
private Long string_speed;
#Column(name = "string_color_type")
private Long string_color_type;
#Column(name = "string_color")
private String string_color;
#Column(name = "string_timing_type")
private String string_timing_type;
#Column(name = "string_timing")
private String string_timing;
#Column(name = "showed")
private Long showed;
#ManyToMany(fetch = FetchType.LAZY,
cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
})
#JoinTable(name = "string_massage",
joinColumns = { #JoinColumn(name = "massage_id") },
inverseJoinColumns = { #JoinColumn(name = "string_id") })
//RstringEntity
#Entity
#Table(name = "string")
public class RstringsEntity {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(name = "name")
private String name;
#Column(name="code")
private String code;
#ManyToMany(fetch = FetchType.LAZY,
cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
}, mappedBy = "strings")
#JsonIgnore
private Set<MasageEntity> masagess = new HashSet<>();
public RstringsEntity() {}

Answer 1

There are multiple ways how to perform queries in Spring Boot: native SQL and JPQL.
In case of native queries we are using pure SQL language, defining query on DB level.
In case of Java Persistence Query Language (JPQL) we define query via entity objects.
Solution 1, native queries
You created the native query in repository, but to use it we need mark it like SQL nativeQuery = true. It required for framework to understang what query laguage do you use. #Query annotation use JPQL by defult, so that's the reason of your errors.
#Repository
public interface MessageRepository extends JpaRepository<MassageEntity, Long> {
//find MessageEntities by String ID via native query
#Query(value = "select massages.* from massages join string_massage on massages.id = string_massage.massage_id where string_massage.string_id = ?1", nativeQuery = true)
List<MassageEntity> findMassagesByStringIdNativeSQL(#Param("strings_id") long strings_id);
//find Message IDs by String ID via native query
#Query(value = "select massages.id from massages join string_massage on massages.id = string_massage.massage_id where string_massage.string_id = ?1", nativeQuery = true)
List<Long> findMassagesIdByStringIdNativeSQL(#Param("strings_id") long strings_id);
}
Solution 2, JPQL queries
Example how to define JPQL queries for your case. JPQL will be translated to SQL during execution.
#Repository
public interface MessageRepository extends JpaRepository<MassageEntity, Long> {
//find MessageEntities by String ID via JPQL
#Query("select message from MassageEntity message join message.strings string where string.id = :strings_id")
List<MassageEntity> findMassagesByStringIdJPQL(#Param("strings_id") long strings_id);
//find Message IDs by String ID via JPQL
#Query("select message.id from MassageEntity message join message.strings string where string.id = :strings_id")
List<Long> findMassagesIDByStringIdJPQL(#Param("strings_id") long strings_id);
}
Native query generated by Hibernate:
select
massageent0_.id as id1_3_,
massageent0_.string_text as string_t2_3_
from
massages massageent0_
inner join
string_massage strings1_
on massageent0_.id=strings1_.massage_id
inner join
string rstringsen2_
on strings1_.string_id=rstringsen2_.id
where
rstringsen2_.id=?
Solution 3, Spring auto-generated queries
Spring can auto-generate queries by repository method definition.
Example for your case:
#Repository
public interface MessageRepository extends JpaRepository<MassageEntity, Long> {
//find MessageEntities by String ID
List<MassageEntity> findByStrings_Id(#Param("id") long strings_id);
}
Entries which I used fro sulutions:
#Entity
#Table(name = "massages")
public class MassageEntity {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(name = "string_text")
private String string_text;
#ManyToMany(fetch = FetchType.LAZY,
cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
})
#JoinTable(name = "string_massage",
joinColumns = { #JoinColumn(name = "massage_id") },
inverseJoinColumns = { #JoinColumn(name = "string_id") })
private Set<RstringsEntity> strings = new HashSet<>();
}
#Entity
#Table(name = "string")
public class RstringsEntity {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(name = "name")
private String name;
#Column(name = "code")
private String code;
#ManyToMany(fetch = FetchType.LAZY,
cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
}, mappedBy = "strings")
#JsonIgnore
private Set<MassageEntity> massages = new HashSet<>();
}