The difference between annotating fields and methods in JPA (Hibernate)?

Question

Are there any statements in JPA spec or official docs about certain JPA implementations which describe the behavior when we annotate entity's methods and when we annotate entity's fields?

Just a few hours ago I met an ugly problem: I use JPA (via Hibernate, but without anything Hybernate-specific in java code) with MS SQL Server. And I put all annotations on entities' fields (I preferred this style until this day).

When I looked at the DB I found that all table columns which should be foreing keys and which should contain some integers (ids) in fact had varbinary(255, null) type and contained hashes of something (I don't know what was that but it looked as a typical MD5 hash).

The most frustrated thing is that the app worked correctly. But occasionally (on updates) I got MS SQL exception which stated that I tried to insert too long values and data cannot be truncated.

Eventually (as an experiment) I removed all annotations from entities fields and put all of them on methods. I recreated DB and all tables contained perfect FK column. And those columns stored integers (ids, like 1, 3 ,4 ...).

So, can somebody explain what was that?

I've found this SO thread and it's accepted answer says that the preferred way is to put annotations on fields. At least for my concrete case I can say that it's not true.

possible duplicate of [Hibernate Annotations - Which is better, field or property access?](http://stackoverflow.com/questions/594597/hibernate-annotations-which-is-better-field-or-property-access) — Pascal Thivent, Jul 21 '10 at 23:21
@Pascal Thivent: I would appreciate if you give an answer based on your experience. I don't claim that there is one preferred way and we should always use it. I noticed absolutely different behavior of my appliation for each of 2 ways of using annotations. And I'm trying to find out what was that: bug or documented in JPA spec/Hibernate docs behavior. — Roman, Jul 21 '10 at 23:26
Field vs property access doesn't change anything from a schema generation point of view (there is nothing about that in the spec, the relevant section is **2.3 Access Type** if you are interested) - at least it shouldn't - and I've never faced the problem you're mentioning. If you can reproduce the problem, submit an issue, this would be a bug. Regarding pros and cons of both approaches, check the duplicate. — Pascal Thivent, Jul 21 '10 at 23:36

score 0 · Answer 1 · answered Mar 12 '13 at 08:00

JPA allows for two types of access to the data of a persistent class. Field access which means that it maps the instance variables (fields) to columns in the database and Property access which means that is uses the getters to determine the property names that will be mapped to the db. What access type it will be used is decided by where you put the @Id annotation (on the id field or the getId() method).

score 0 · Answer 2 · edited Feb 14 '14 at 15:57

From experience, I do the following.

I put the entity details at the top of the entity class definition, (schema, row constraints, etc) for instance....

@Entity
@Table(name="MY_TABLE", schema = "MY_SCHEMA", uniqueConstraints = @UniqueConstraint(columnNames = "CONSTRAINT1"))

For the fields defined, I do not put the annotations on the field declarations, but rather on the getter methods for those fields

@Column(name = "MY_COL", table="MY_TABLE", nullable = false, length = 35)
public String getMyCol() {
    return this.myCol;
}

public void setMyCol(String myCol) {
    this.myCol = myCol;
}

The difference between annotating fields and methods in JPA (Hibernate)?

2 Answers2