composite-primary-key

问题 Does anybody knows any performance issues in using composite-ids, whether @EmbeddedId or @IdClass , with Hibernate? Thanks. 回答1: In my opinion, Hibernate itself does not have significant performance impact whether its a composite key or not. what matters is the dbms, engine type, queries, number of updates on table, indexes and types of columns. Hibernate will just be translating hql into sql, so in this case performance of hibernate should be good if underlying queries perform good.... here

问题 I have an additional question related to post: Composite primary keys in databases Please check out the post over there (otherwise I just need to repeat it). Now my question is: If I go for an ID autoincrement as primary key (as I accepted and which allows me to again reference the current table through this key), how can I assure that a combination between User_ID and Admin_ID (both FK's) can only exist once (is unique ) on insert? It is a many-to-many relationship. It could be done in the

问题 I need to create a database design where bar or event owners (admin-table because they own a profile) send alerts to users. I want to create an "ALERT" table but have a hard time deciding what primary key to use. I thought adding a composite key containing at least admin_ID (PFK), user_ID (PFK) and I thought to add Date and Time stamp to the primary key to indicate that many alerts (notifications) can be sent by an admin, but only 1 at a certain point in time. However, from this thread:

问题 I have created the following 3 tables using the following code. CREATE TABLE BUILDING( BUILDINGNO CHAR(2), BUILDINGWING VARCHAR2(15), BUILDINGLANE VARCHAR2(15), CONSTRAINT BUILDING_PK PRIMARY KEY(BUILDINGNO)); CREATE TABLE ROOM( BUILDINGNO CHAR(2), ROOMNO CHAR(2), ROOMCAPACITY NUMBER(3), CONSTRAINT ROOM_PK PRIMARY KEY(BUILDINGNO,ROOMNO), CONSTRAINT ROOM_FK1 FOREIGN KEY(BUILDINGNO) REFERENCES BUILDING(BUILDINGNO)); CREATE TABLE SPEAKER( SPEAKERID CHAR(2), SPEAKERNAME VARCHAR2(20),

问题 We are trying to use Hibernate with a database that uses a lot of composite keys and it's been causing us a lot of headaches. Unfortunately, we can't change the schema so we have to do a lot of additional mapping betwen our fields. We are restricted to using JPA 1.0 and Hibernate 3.3. The biggest problem we've had so far is to do with a one-to-one association between two entities using a composite key of 2 values, where the tables have different names for these columns (the DB has a naming

问题 I have 3 tables in Oracle (10g). Zone Weight ZoneCharge Where ZoneCharge has a composite primary key(zoneId, weightId) which references to primary keys of the Zone and the Weight tables. I need to delete all the rows from the ZoneCharge table based on the zoneId supplied (the weightIds are unknown in this case). The native Oracle SQL to achieve this would be as simple as follows. DELETE FROM zone_charge WHERE zone_id=22; I have tried the following way (in DAO). @Override @SuppressWarnings(

问题 I get this error when using linq-to-sql with timestamp as part of a composite primary key: "The primary key column of type 'Timestamp' cannot be generated by the server." I'm guessing this may be due to the fact timestamp is just a row version thus perhaps it must be created after the insert? Or... 回答1: You can work around it.. set Auto Generated Value to True Auto-Sync to OnInsert ...unless you already have of course 回答2: don't use the timestamp data type!! The timestamp syntax is deprecated

问题 I would like to know if there is a real case scenario in which race condition problems can actually occur on an insertion query. So I have a table "User" with the following fields: User: iduser | idcompany | name | email I use a composite primary key for this table that is (iduser, idcompany). None of these fields is set to AUTO_INCREMENT. I get the value of the field "idcompany" through a session variable, so there's is not a real problem in this. However, I use a getNextUserId() function to

问题 I'm attempting to setup a foreign key in table cell_lines that will reference the topographic_region column of the composite primary key in table topographic_regions . Each time I run the last three lines of code trying to add the foreign key, I receive Error Code 1215: cannot add foreign key constraint. Now, the foreign key column name ( topographic_region ) in cell_lines only matches one of the composite primary key column names in topographic_regions , the other composite primary key

问题 I Have two Tables. CREATE TABLE One( Oneid int, Twoid int, data char(20), PRIMARY KEY(Oneid,Twoid) ) Table One is Oneid and Twoid as primary key. CREATE TABLE Two( Twoid int, data char(20), PRIMARY KEY(Twoid) ) And I want to One.Twoid is foreign key for Table Two. How to solve it. Thank a lot. 回答1: Add the constraint in the CREATE TABLE statement: CREATE TABLE Two( Twoid int, data char(20), PRIMARY KEY (Twoid)); CREATE TABLE One( Oneid int, Twoid int, data char(20), PRIMARY KEY (Oneid,Twoid),