Hibernate show real SQL
log4j.properties hibernate.cfg.xml persistence.xml Some frameworks use persistence.xml:
orm
How to map a composite key with JPA and Hibernate?
To map a composite key, you can use the EmbeddedId or the IdClass annotations. I know this question is not strictly about JPA but the rules defined by the specification also applies. So here they are: 2.1.4 Primary Keys and Entity Identity … A composite primary key must correspond to either a single persistent field or property or to a … Read more
What’s the difference between JPA and Hibernate?
I understand that JPA 2 is a specification and Hibernate is a tool for ORM. Also, I understand that Hibernate has more features than JPA 2. But from a practical point of view, what really is the difference? I have experience using iBatis and now I’m trying to learn either Hibernate or JPA2. I picked … Read more
Advice on loopback.js vs express js
Planning to build an enterprise level application using node js. Have already worked on express js for a few projects. When researching for other possible frameworks, came across loopback js. Loopback.js, a new framework(3-4 years) built over express framework. The initial configuration and set up of the application was so quick, as i able to … Read more
Hibernate throws org.hibernate.AnnotationException: No identifier specified for entity: com..domain.idea.MAE_MFEView
You are missing a field annotated with @Id. Each @Entity needs an @Id – this is the primary key in the database. If you don’t want your entity to be persisted in a separate table, but rather be a part of other entities, you can use @Embeddable instead of @Entity. If you want simply a … Read more
Conversion of a datetime2 data type to a datetime data type results out-of-range value
This can happen if you do not assign a value to a DateTime field when the field does not accept NULL values. That fixed it for me!
How to fix the Hibernate “object references an unsaved transient instance – save the transient instance before flushing” error
You should include cascade=”all” (if using xml) or cascade=CascadeType.ALL (if using annotations) on your collection mapping. This happens because you have a collection in your entity, and that collection has one or more items which are not present in the database. By specifying the above options you tell hibernate to save them to the database when saving their parent.
What is the “N+1 selects problem” in ORM (Object-Relational Mapping)?
Let’s say you have a collection of Car objects (database rows), and each Car has a collection of Wheel objects (also rows). In other words, Car → Wheel is a 1-to-many relationship. Now, let’s say you need to iterate through all the cars, and for each one, print out a list of the wheels. The naive O/R implementation would do the following: And then for each Car: … Read more
How to fix the Hibernate “object references an unsaved transient instance – save the transient instance before flushing” error
You should include cascade=”all” (if using xml) or cascade=CascadeType.ALL (if using annotations) on your collection mapping. This happens because you have a collection in your entity, and that collection has one or more items which are not present in the database. By specifying the above options you tell hibernate to save them to the database when saving their parent.
sequelize “findbyid” is not a function but apparently “findAll” is
With Sequelize v5, findById() was replaced by findByPk(). Replace findById using findByPk and everything should work fine. You can find query doc here