I am using Hibernate in my project. I have a database schema already created.
I see in the tutorials online
#Column(name = "STOCK_ID", unique = true, nullable = false)
public Integer getStockId() {
return this.stockId;
}
the columns properties like unique nullable etc are being used. My question is do I need to
specify these properties when I already have a db schema prepared prehand with the columns being given all the not null and all the checks while creating the tables?.
No you don't, only the required parameters in the Hibernate annotations have to be filled in. But the optional parameters frequently have default values. Your DB will have to be compatible with the default values, else you will have to fill in the values you use.
unique is only used when generating the database schema from the JPA annotations. nullable = false allows JPA to be more efficient: if the value is null when it writes the entity to the database, it doesn't even have to execute the insert/update query and can throw an exception immediately.
Even if that's not absolutely necessary, I like having these informations in the mapping for documentation purposes. Being able to know immediately from the code, without looking at the database schema, that an attribute is nullable or not, is useful.
Related
I have property in Enum:
#Basic
#Column(name = "payment_status", columnDefinition = "varchar(32) default 'ENTERED'", nullable = false)
#Enumerated(EnumType.STRING)
private PaymentStatus paymentStatus;
I want to get the default value for a field from enum
I have error:
org.hibernate.PropertyValueException: not-null property references a null or transient value
The field cannot be null
The error is when I want to create an object and save in the database without entering this field (PaymentStatus)
EDIT:
#Basic
#ColumnDefault(value = "ENTERED")
#Column(name = "payment_status", nullable = false)
#Enumerated(EnumType.STRING)
private PaymentStatus paymentStatus = PaymentStatus.ENTERED;
Why is it not working?
default 'ENTERED' tells the database to use value 'ENTERED' if the column is not included in the INSERT statement. Since the column is in the class, JPA will always include it in the INSERT statement.
To make JPA fill in the default value, simply assign it with an initializer, so it has that value until replaced by you (calling setter method), or replaced from database (when reading from there).
private PaymentStatus paymentStatus = PaymentStatus.ENTERED;
If you have defined a default in the database and if you want to leave it to the database to set the default value then you need to prevent a null being inserted to that column in the SQL insert statement
You would then need to look at what your JPA provider offers in that area. In Hibernate, for example, you would simply annotate your Entity with #DynamicInsert:
https://docs.jboss.org/hibernate/orm/5.2/javadocs/org/hibernate/annotations/DynamicInsert.html
For inserting, should this entity use dynamic sql generation where
only non-null columns get referenced in the prepared sql statement?
It should be noted that defining a default in the JPA annotations (as you have done) only has any effect on DDL generation i.e. if you are having your JPA provider generate or update your schema and has to effect on any insert or update operations.
I am using Hibernate as my JPA provider, and I want one of the fields in an entity to be ignored when calling save(). However, I do have a matching column in the corresponding database table and I want my entity field to be populated with the database value when I fetch the entity. So, I want the field to be ignored when saving the entity, but not when fetching it.
If I use #Transient, the field is completely ignored, which is not what I want. Is there any way to do this?
From the excellent book Pro JPA 2 :
JPA defines options to set individual mappings to be read-only using
the insertable and updatable elements of the #Column and #JoinColumn
annotations. These two settings default to true but can be set to
false if we want to ensure that the provider will not insert or update
information in the table in response to changes in the entity
instance. If the data in the mapped table already exists and we want
to ensure that it will not be modified at runtime, then the
insertable and updatable elements can be set to false, effectively
preventing the provider from doing anything other than reading the
entity from the database.
#Column(insertable = false, updatable = false)
private String readOnlyField;
I know there are plenty of these questions here on SO and also on the net, but all the answers suggest using columnDefinition which is database specific and hence not applicable for me because the system I'm working on needs to run on different databases.
I found this hibernate issue where someone requested this feature for annotations. The issue has been closed saying that another issue will cover that functionality. The second issue apparently added annotation #Generated and also some others, but I couldn't find any documentation on how to define the default column value with those new annotations.
So my question is: Does anyone know how can I define a default column value with annotations (and NOT using columnDefinition)?
Edit: to further clarify my problem: When I add a new not null column, I need Hibernate to update the existing schema (add the new column to the respective table). But since the column is non null, the database cannot create the column without specifying the default value (if there are already some rows in the table). So I need to instruct Hibernate to issue the following DDL statement: ALTER TABLE my_table ADD COLUMN new_column VARCHAR(3) DEFAULT 'def', but it has to be independent of the used database.
I don't think you need any documentation, the java docs are self explaining.
If I understand you correctly you need a way to set a default value for a field. If yes please see the following code snippet.
#Entity
#Table(name = "my_entity")
public class SomeEntity extends BaseEntity {
public static final class MyValueGenerator implements
ValueGenerator<String> {
#Override
public String generateValue(Session session, Object owner) {
return "This is my default name";
}
}
#Basic
#Column(name = "name", insertable = true, updatable = true, nullable = false, length = 255)
// This will add a DDL default
#ColumnDefault("'This is my default name'")
// This will add a runtime default.
#GeneratorType(type = MyValueGenerator.class)
private String name;
// getters and setters
}
Following is working for me.
#ColumnDefault("'0.0'")
#Column(name = "avgRating")
private float avgRating;
I am reviewing the code of a colleague. In his entity object he has set nullable = false and he is also checking in the setter that the value to set is not null.
Is this useful? In any case, the nullable = false will throw an exception at some point.
(The checkArgumentNotNull will throw an illegal argument exception if the value is null.)
private TypeChampMaterielDefaillant typeChamp;
#Column(name = "TYPE_CHAMP", nullable = false, length = 30)
#Enumerated(EnumType.STRING)
public TypeChampMaterielDefaillant getTypeChamp() {
return typeChamp;
}
public void setTypeChamp(TypeChampMaterielDefaillant typeChamp) {
checkArgumentNotNull(typeChamp, "typeChamp");
this.typeChamp = typeChamp;
}
EDIT
So if I understand correctly nullable=false only apply to schema generation, thus if the database is not generated with the current entity it will be possible to persist a null value
Parameter nullable = false will happen on database operation (you won't be able so persist entity with this value equals to null). Additional check in setter is useful because you'll get exception earlier (during setter invocation) but not necessary.
I would say nullable = false is used for schema generation, not for validation from jpa(unless some third party library uses for validating before persist)
JPA 2.1 Specification:
11.2.2.1 Column
The following elements of the Column annotation are used in schema generation:
name
unique
nullable
columnDefinition
table
length (string-valued columns only)
precision (exact numeric (decimal/numeric) columns only)
scale (exact numeric (decimal/numeric) columns only)
See section 11.1.9 for the rules that apply to these elements and column creation. The AttributeOverride annotation may be used to override column
mappings.
As you can see jpa spec talks nothing about validation, unless hibernate/or some third party does. I am not positive either about hibernate validator for that nullable = false statement.
You better use some validator framework or use #PrePersist, #PreUpdate annotations.
Setter validation also bad, how about if user does not call it at all ?
No, this is very bad practice. A Hibernate-Bean is a bean, any kind of intelligent setter is an workaround anyway.
Use the annotations instead like #NotNull!
Use asserations if you realy need something that is thrown in test/devel!
I don't understand at all the difference between these annotations.
Could you please explain me if this is redundant?
#NotNull
#Basic(optional = false)
#Column(nullable = false)
private int userId;
Thanks in advance.
#NotNull : This annotation you are defining that your code will not except a null parameter, if you were to provide a null parameter, the annotation would throw a RuntimeException.
#Basic : This annotation signifies that an attribute is to be persisted and a standard mapping is to be used. It has parameters which allow you to specify whether the attribute is to be lazily loaded and whether it's nullable.
#Column allows you to specify the name of the column in the database to which the attribute is to be persisted.
Here are the difference that I noticed.
#NotNull comes from javax.validation JSR303 it define if the property of the bean can be null, set this indicate that property can not be null, this are called constraints and are verified in validation.validate() method.
#Basic(optional = false) comes from javax.persistence JSR317, there are Basic types and collection Types it indicate the logical model can be null or not set optional to false indicate that the propery can not be null at jpa logical model. Also allows you to declare the fetching strategy for a property
#Column(nullable = false) comes from javax.persistence JSR317, it is related to physical mapping with the database (DDL) telling to the database that the property can not be null in the database. (NOT NULL statement in table creation)
As you can see first one works with Validation API, second and third apply to JPA API but one in the logical and the other in the physical mode.