12/30/2023 0 Comments Hibernate java sqlYou can use to define a base class that will be extended by all entities: class BaseEntity Long = LocalDateTime = "created_by") Hibernate offers the and annotations that can be used to map the created_on and updated_on columns. Let's assume you have the following database tables: You can allow the database to do that.įor the create_on column, you could use a DEFAULT DDL constraint, like : ALTER TABLE postĭEFAULT CURRENT_TIMESTAMP() FOR created_on įor the updated_on column, you could use a DB trigger to set the column value with CURRENT_TIMESTAMP() every time a given row is modified. What annotations would you use for the mapping (e.g. Whom would you make responsible for setting the timestamps-the database, the ORM framework (Hibernate), or the application programmer? Only if you are using, you need to specify the annotation, like this: = "created_on")īut, it's much better if you map it like this: = "created_on") you are using the LocalDateTime or to map a timestamp entity property, then you don't need to use since HIbernate already knows that this property is to be saved as a JDBC Timestamp. You can also use the legacy Date, but the Java 8 Date/Time types are better since they are immutable, and don't do a timezone shifting to local timezone when logging them. On the Java side, you can use the Java 8 LocalDateTime. What data types would you use in Java (Date, Calendar, long. What entity property type you should use.So, for this reason, it's best to use UTC on the database side and use the _zone Hibernate property. So, better to use DATETIME instead, which doesn't have this upper boundary limitation. In MySQL, the TIMESTAMP column type does a shifting from the JDBC driver local time zone to the database timezone, but it can only store timestamps up to 03:14:07.999999, so it's not the best choice for the future. What data types would you use in the database (assuming MySQL, possibly in a different timezone that the JVM)? Will the data types be timezone-aware? What database column types you should use.The following form is not vulnerable to column nameĭuplication: sess. Specified in the mappings ("ID" and "NAME"). The query will, however, fail because there is aĬonflict of names the instances are mapped to the same column names.Īlso, on some databases the returned column aliases will most likely be The query was intended to return two Cat instances per row: a catĪnd its mother. Most likely will fail): sess.createSQLQuery("SELECT c.*, m.* FROM CATS c, CATS m WHERE c.MOTHER_ID = c.ID") Problematic for SQL queries that join multiple tables, since the sameĬolumn names can appear in more than one table.Ĭolumn alias injection is needed in the following query (which Until now, the result set column names are assumed to be the sameĪs the column names specified in the mapping document. Of the same type or when the default alias/column names are not Problems can arise when returning multiple entities Native queries, without starting to enhance the sql queries to make them sess.createSQLQuery("SELECT ID, NAME, BIRTHDATE, D_ID, D_NAME, CAT_ID FROM CATS c, DOGS d WHERE c.ID = d.CAT_ID")Īt this stage you are reaching the limits of what is possible with Is possible to do the same eager joining for collections, e.g. ("cat") to be able to specify the target property path of the join. Their dog property fully initialized without anyĮxtra roundtrip to the database. In this example, the returned Cat's will have sess.createSQLQuery("SELECT c.ID, NAME, BIRTHDATE, DOG_ID, D_ID, D_NAME FROM CATS c, DOGS d WHERE c.DOG_ID = d.D_ID") This isĭone via the addJoin() method, which allows you to It is possible to eagerly join in the Dog toĪvoid the possible extra roundtrip for initializing the proxy. Not mapped, or does not result in the expected type, it is possible toĬustomize it via calls to registerHibernateType inġ6.1.3. Handling associations and collections To Hibernate types is controlled by the Dialect. How the returned from ResultSetMetaData is mapped NAME and BIRTHDATE, where as the type of ID is explicitly ResultSetMetaData is used to determine the type of This is essentially the same query as before, but now sess.createSQLQuery("SELECT * FROM CATS") It is possible to leave out the type information for all or some * and could return more than the three listed This also means that only these threeĬolumns will be returned, even though the query is using ID, NAME and BIRTHDATE column as respectively a Long, String and a Shortįrom the underlying resultset. ResultSetMetadata but will instead explicitly get the This will return Object arrays, but now it will not use
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