Some clarification on the Hibernate save() method. Why correctly update an existing record?

Question

I am pretty new in Hibernate and I have the following doubt.

Into a database table named TWP1007_PROGETTO I have this row (but the content is not important at this time):

PRG_PRO COD_MEC_ATT DAT_ANN_SCO_ATT COD_MEC_INI_PRO COD_PRO IMP_FIN COD_TIP_STA FLG_TIP_PRG PRG_GRA_WIF PRG_GRA_PNS FLG_PRE_FIR_DIR FLG_PRE_FIR_REV DAT_INS_REN DESC_NOM_FIL_REN    OGG_FIL_REN DAT_VAL DES_NOT_VAL DAT_TRA_UFF_LIQ IMP_TOT_SPE IMP_SAL DES_NOM_UTE_VAL DES_NOM_DIR_REN DAT_ORA_ULT_MOV COD_PGM_ULT_MOV COD_UTE_ULT_MOV
2   AGIS018009  201516  AGIS018009  Progetto Wifi   7980,00 4   W   2                               null                    12/10/2015 00:00:00 Rimesso in lavorazione  user.name

Then, into a Spring MVC service class, I have create this method to update a record of this table:

public void rimettiInLavorazioneProgetto(Twp1007Progetto progetto) {
    progettoRepo.save(progetto);
}

Where (Twp1007Progetto progetto is the object that map the TWP1007_PROGETTO table).

So as you can see in the previous method I use the save() hibernate method.

It works and the record is correctly updated but it seems strange because from what I have understand the save() method have to create a new record whereas the update() method have to update an existing record.

So why it works? Why it correctly update an existing record?

Answer 1

Yes. Save() method do create new record if and only if your Object don't have an generated identifier

Persist the given transient instance, first assigning a generated identifier. (Or using the current value of the identifier property if the assigned generator is used.)

If you have already a generated identifier associated with your Object, it just saves to that row.