Nested one to many relationship jpa spring boot - mysql

Question

I have three classes - Document, Page, Sentence. A Document will have multiple Pages & each Page will have multiple Sentences. I'm trying to map One to Many relationship using Spring Data JPA annotation. But it only works when there are only one layer like - Document>Page. Doesn't work while it's Document>Page>Sentence.
Can anyone please give me a solution for how to do it for nested one to many relationship ?
My classes are given below.
#Entity
#Table(name = "DOCUMENT")
public class Document implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#Column(name = "FILEID")
#GeneratedValue(strategy = GenerationType.AUTO)
private long idFile;
#Lob
#Column(name = "CONTENT")
private byte[] content;
#Column(name = "NAME")
private String name;
#Column(name = "ID_MAIL_USER")
private String idMailUser;
#Column(name = "NUM_PAGES")
private int numPages;
#Column(name = "TO_ANALIZE")
private boolean toAnalize;
#Column(name = "HASH")
private String hash;
#Column(name = "EXTENSION")
private String extension;
#Column(name = "SIZE")
private double size;
#Column(name = "LINK_TO_DRIVE_FILE")
private String linkToDriveFile;
#Column(name="PATH")
private String path;
#OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
#Column(name = "PAGES")
private List<Page> pages = new ArrayList<>();
// Setter Getters
}
.
#Entity
#Table(name = "PAGE")
public class Page implements Serializable {
#Id
#Column(name = "PAGE_ID")
#GeneratedValue(strategy = GenerationType.AUTO)
private long idPage;
#Column(name = "PAGE_NUMBER")
private int pageNum;
#Lob
#Column(name = "CONTENT")
private String content;
#ManyToMany(cascade = CascadeType.ALL)
#Column(name = "SENTENCES")
private List<Sentence> sentences = new ArrayList<>();
// Setter Getters
}
.
#Entity
#Table(name = "SENTENCE")
public class Sentence implements Serializable {
//private long idFile;
//private long idPage;
#Id
#Column(name = "SENTENCE_ID")
#GeneratedValue(strategy = GenerationType.AUTO)
private long id;
#Column(name = "PAGE_NUMBER")
private int pageNumber;
#Column(name = "ORDER")
private int ord;
#Column(name = "CONTENT")
private String content;
#Column(name = "HASH")
private String hash;
// Setter Getters
}

Answer 1

Your OneToMany mappings are incorrect. Correct it as follows
#Entity
#Table(name = "DOCUMENT")
public class Document implements Serializable {
......
#OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
#JoinColumn(name = "DOCUMENT_ID") //Name the foreign key column in PAGE table to DOCUMENT_ID
private List<Page> pages = new ArrayList<>();
}
#Entity
#Table(name = "PAGE")
public class Page implements Serializable {
....
#OneToMany(cascade = CascadeType.ALL)
#JoinColumn(name = "PAGE_ID") //Name the forein key column in PAGE table to PAGE_ID
private List<Sentence> sentences = new ArrayList<>();
}
Use #JoinColumn annotation instead of #Column to give the name of the foreign key that do the physical mapping between tables in your database.

Answer 2

#Entity
#Table(name = "DOCUMENT")
public class Document implements Serializable {
private static final long serialVersionUID = 1L;
#OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, mappedBy="document")
#Column(name = "PAGES")
private List<Page> pages = new ArrayList<>();
}
#Entity
#Table(name = "PAGE")
public class Page implements Serializable {
#ManyToOne
#JoinColumn(name="DOCUMENT_ID")
private Document document;
#ManyToMany(cascade = CascadeType.ALL, mappedBy="pages")
#Column(name = "SENTENCES")
private List<Sentence> sentences = new ArrayList<>();
}
#Entity
#Table(name = "SENTENCE")
public class Sentence implements Serializable {
#ManyToMany(mappedBy="sentences")
private List<Page> pages;
}
Here a Document One to Many relationship with Pages.
So.. we need define mappedBy in the entity we want to map another entity.. so in this case
#OneToMany(mappedBy="document",cascade = CascadeType.ALL, orphanRemoval = true)
and in referenced entity i.e. Pages we want foreign key DOCUMENT_ID, so we have to define it using
#ManyToOne
#JoinColumn(name="DOCUMENT_ID")