java - Hibernate/JPA many-to-many relation through 2 intermediate tables -

i have following case (in different domain described, analogical , more comprehensive think) - db history of people presence in buildings:

• people generating signals based on current detected location (all captured signals stored in locationsingal table).
• some of these signals recognized events - when detected around building's gates (gates not on model diagram simplicity). full history of such events stored in detectionevent table (and additional detectioneventhistory table temporal distinction of similar records).
• based on business logic of these events identified person's entry/exit to/from buildings , stored in presence table (with full historical register of presence changes based on additional presencehistory table).

db schema [only minimum of table fields]:

question 1: proper orm (based on hibernate/jpa api) allow access detectionevent object directly presence object? there mapping:

• entry_detectioneventhistory_id table field => entrydetectionevent object reference
• exit_detectioneventhistory_id table field => exitdetectionevent object reference

... considering person_id detectionevent equal person_id presence.

this kind of many-to-many relationship between these tables through 2 intermediate , independent tables (detectioneventhistory , person). documentation examples focus on single intermediate table kind of relation.

i know can calculate on demand every presence object, utilizing @manytoone , @onetomany mappings sequentially, adding these methods presence class:

public detectionevent getentrydetectionevent() {     return entrydetectioneventhistory.getdetectioneventfor(person.getid()); }  public detectionevent getexitdetectionevent() {     return exitdetectioneventhistory.getdetectioneventfor(person.getid()); } 

... , additional getdetectioneventfor(...) method detectioneventhistory class:

@jsonignore public detectionevent getdetectioneventfor(long personid) {     (detectionevent detectionevent : detectioneventlist) {         if (detectionevent.getperson().getid() == personid) {             return detectionevent;         }     }      return null; } 

... , i'll desired detectionevent object. seems highly inefficient when fetching list of presence records. there additional query executed twice per each such object: entry/exit detection event (e.g. when such list has serialized publishing rest api). plus automated mapping of generated in such way exitdetectionevent = null (a valid case when person entered did not exit) json kind of issue me here.

i guess define dao based on query joining these tables additional data bean - variation of presence entity bean. maybe there simpler way. so...

question 2: can done more effectively? suggestions appreciated...

jpa model is:

@entity @table(name = "locationsignal") public class locationsignal implements serializable {     private static final long serialversionuid = 1l;      @id     @generatedvalue(strategy = generationtype.sequence)     @column(name = "id")     private long id;      @column(name = "details")     private string details;      @onetomany(mappedby = "locationsignal", cascade = cascadetype.all, fetch = fetchtype.lazy)     private list<detectionevent> detectioneventlist = new arraylist<>(); }  @entity @table(name = "person") public class person implements serializable {     private static final long serialversionuid = 1l;      @id     @generatedvalue(strategy = generationtype.sequence)     @column(name = "id")     private long id;      @onetomany(mappedby = "person", cascade = cascadetype.all, fetch = fetchtype.lazy)     private list<detectionevent> detectioneventlist = new arraylist<>();      @onetomany(mappedby = "person", cascade = cascadetype.all, fetch = fetchtype.lazy)     private list<presence> presencelist = new arraylist<>();      public long getid() {         return id;     } }  @entity @table(name = "building") public class building implements serializable {     private static final long serialversionuid = 1l;      @id     @generatedvalue(strategy = generationtype.sequence)     @column(name = "id")     private long id;      @onetomany(mappedby = "building", cascade = cascadetype.all, fetch = fetchtype.lazy)     private list<presence> presencelist = new arraylist<>(); }  @entity @table(name = "detectionevent") public class detectionevent implements serializable {     private static final long serialversionuid = 1l;      @id     @manytoone()     @joincolumn(name = "person_id", referencedcolumnname = "id")     private person person;      @id     @manytoone()     @joincolumn(name = "detectioneventhistory_id", referencedcolumnname = "id")     private detectioneventhistory detectioneventhistory;      @manytoone()     @joincolumn(name = "locationsignal_id", referencedcolumnname = "id")     private locationsignal locationsignal;      public person getperson() {         return person;     } }  @entity @table(name = "detectioneventhistory") public class detectioneventhistory implements serializable {     private static final long serialversionuid = 1l;      @id     @generatedvalue(strategy = generationtype.sequence)     @column(name = "id")     private long id;      @column(name = "timestamp")     private timestamp timestamp;      @onetomany(mappedby = "detectionevent", cascade = cascadetype.all, fetch = fetchtype.lazy)     private list<detectionevent> detectioneventlist = new arraylist<>();      @onetomany(mappedby = "entrydetectioneventhistory", cascade = cascadetype.all, fetch = fetchtype.lazy)     private list<presence> entrydetectioneventhistorylist = new arraylist<>();      @onetomany(mappedby = "exitdetectioneventhistory", cascade = cascadetype.all, fetch = fetchtype.lazy)     private list<presence> exitdetectioneventhistorylist = new arraylist<>(); }  @entity @table(name = "presence") public class presence implements serializable {     private static final long serialversionuid = 1l;      @id     @manytoone()     @joincolumn(name = "person_id", referencedcolumnname = "id")     private person person;      @id     @manytoone()     @joincolumn(name = "building_id", referencedcolumnname = "id")     private building building;      @id     @manytoone()     @joincolumn(name = "presencehistory_id", referencedcolumnname = "id")     private presencehistory presencehistory;      @manytoone()     @joincolumn(name = "entry_detectioneventhistory_id", referencedcolumnname = "id")     private detectioneventhistory entrydetectioneventhistory;      @manytoone()     @joincolumn(name = "exit_detectioneventhistory_id", referencedcolumnname = "id")     private detectioneventhistory exitdetectioneventhistory; }  @entity @table(name = "presencehistory") public class presencehistory implements serializable {     private static final long serialversionuid = 1l;      @id     @generatedvalue(strategy = generationtype.sequence)     @column(name = "id")     private long id;      @column(name = "timestamp")     private timestamp timestamp;      @onetomany(mappedby = "presencehistory", cascade = cascadetype.all, fetch = fetchtype.lazy)     private list<presence> presencelist = new arraylist<>(); }