So I've read tons and tons of posts, forums, question and answers about this topic but I am still quite unsure about what migration means.
Let me first introduce you to my problem.
I have a Spring Boot backend working with MySQL Database with the help of Spring JPA Entities.
Now my problem is the following:
I already have a Spring JPA Entity defined as follows:
#Entity
#Getter
#Setter
public class Blog {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String title;
private String content;
private LocalDateTime createdAt = LocalDateTime.now();
}
After having this entity persisted to the database, I realized that the simple String title wouldn't be enough as it maps to a varchar(255) making my Blog posts couldn't exceed 255 characters.
So I would like to change this in the database without running any custom built SQL scripts to modify the column type in the table.
I have something in mind like I would modify the current JPA Entity as follows:
#Entity
#Getter
#Setter
public class Blog {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String title;
#Lob // <--- Notice the Lob here
private String content;
private LocalDateTime createdAt = LocalDateTime.now();
}
If I am right, the Large Object annotation would mean that in the Database the column type becomes longtext allowing a lot more characters than 255 so my blog posts would fit.
So in short this is how I stumbled upon the topic of Database Migration I am just unsure if that is the thing I need in this situation. Can you please confirm if I am right about this, also can you please suggest possible solutions for this particular problem? I know there is a tool called Liquibase used for migrations which is quite popular. Should I go for it, or is there somthing else I would need?
Thanks in advance for the help.
I built an application with Quarkus and I'm using Hibernate with Panache for the models. Everything goes well, the application starts, but when I call a webservice to get a list using Panache functionalities (.listAll()), I get an empty list and I see the following message in the console:
HHH000183: no persistent classes found for query class: from com.myproject.model.TeamEntity
My models are defined with #Entity annotations that should allow Hibernate to find by itself the entity mappings. Here is an example with the Team model:
#Entity
#Table(name = "TEAM")
public class TeamEntity extends PanacheEntityBase {
#Id
#GeneratedValue(strategy = SEQUENCE, generator = "TEAM_SEQ_GEN")
#SequenceGenerator(name = "TEAM_SEQ_GEN", sequenceName = "TEAM_SEQ", allocationSize = 10)
#Column(name = "ID_TEAM", nullable = false)
private int id;
#Column(name = "NAME", nullable = false)
private String name;
...
}
I don't have any persistence.xml file in the project, only the application.properties linked with Quarkus. Here are the relevant properties extracted from mine:
quarkus.datasource.db-kind=oracle
quarkus.datasource.jdbc.url=jdbc:oracle:thin:/#MYWALLET
%dev.quarkus.datasource.jdbc.url=jdbc:oracle:thin:MYUSER/MYPASSWORD#localhost:1521/SAA
quarkus.datasource.jdbc.driver=oracle.jdbc.OracleDriver
quarkus.datasource.jdbc.min-size=2
quarkus.datasource.jdbc.max-size=10
quarkus.datasource.jdbc.new-connection-sql=alter session set current_schema=MYSCHEMA
quarkus.hibernate-orm.dialect=org.hibernate.dialect.Oracle12cDialect
Does someone know where the problem could come from ? Hibernate should detect entities with annotations and use them in queries automatically.
It came out that the problem was on Quarkus Datasource configuration in the application.properties file. More particularly from this specific line to define the schema used at first connection (I have to admit that was not good looking):
quarkus.datasource.jdbc.new-connection-sql=alter session set current_schema=MYSCHEMA
Replacing the line above with the following solved the problem:
quarkus.hibernate-orm.database.default-schema=MYSCHEMA
In conclusion, I think Hibernate cannot find / does not take the entities defined if this property is not defined, maybe because it makes some kind of detection beforehand. That's only a supposition, if someone knows more precisely how Hibernate works for that specific case, I would be very interested !
I made a NamedQuery that works but I have multiple error markers in eclipse. Now my query might not be legal, an answer of so (see comments) told me it wasn't possible to do what I intended to do in jpa. So, since I managed to do it anyway and I don't really have a clue why it works: my question is what are the underlying risks of using this :
query = "SELECT t FROM Thethread t LEFT JOIN FETCH t.threadVotes tv ON tv.user1=:currentUser ORDER BY t.datePosted DESC"
Under on:
JOIN FETCH expressions cannot be defined with an identification
Under :currentUser:
Input parameters can only be used in the WHERE clause or HAVING clause of a query.
I didn't manage to get the result I want without it. Which is :
Get the newest Thethread
Get only the current user vote in its collection.
If you know how to do that, please, be my guest.
The entities are as such :
public class Thethread implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private long idthread;
#Temporal(TemporalType.TIMESTAMP)
#Column(name = "date_posted")
private Date datePosted;
private int downvotes;
private int upvotes;
// bi-directional many-to-one association to ThreadVote
#OneToMany(mappedBy = "thethread")
private List<ThreadVote> threadVotes;
}
public class ThreadVote implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#Column(name = "id_votes_thread")
private int idVotesThread;
private int vote;
// bi-directional many-to-one association to Thethread
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "thread")
private Thethread thethread;
// bi-directional many-to-one association to User
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "from_user")
private User user1;
}
Your query is correct JPQL according to JPA 2.1 (JavaEE 7). Eclipselink supports it and other providers should too, if they support 2.1 version of JPA.
The operator ON with JOIN is new with this latest JPA version, it was not present in neither JPA 2.0 (JavaEE 6) nor in older JPA 1 versions.
Here is more info from EclipseLink wiki. The wiki states that Eclipselink implements ON operator and that it is in draft JPA 2.1. I checked also that it is also in final JPA 2.1 specification - and it is there.
In order to use your query, you just need to ensure that your environment/application server supports JPA 2.1 (e.g. application server should support Java EE 7, such as Glassfish 4 or WildFly 8+)
It is not a problem that your IDE (Eclipse) gives warnings until your query works. Eclipse probably does not support JPA 2.1 syntax or your project must be somehow configured to support JPA 2.1 and not older versions of JPA. Try to look into project properties, under project facets, and ensure you have JPA in version 2.1
I have entity that has a version. It has composite primary key where one part of it is id of an entity and other is version. I want to create many-to-one mapping to this entity, and I need to have the latest version on the many side of this mapping.
For example:
#Entity
#IdClass(VersionedId.class)
class SomeVersionedComponent {
private Long id;
private long version;
...
}
#Entity
class ManyMappingSide {
private Long id;
private SomeVersionedComponent component;
#ManyToOne ///????
public SomeVersionedComponent getComponent() {...}
public void setComponent(SomeVersionedComponent component) {...}
}
I do not need to save version information in ManyMapingSide, I just need to have only id, and when ManyMappingSide is loaded I want to have the latest version of SomeVersionedComponent.
How can I implement it?
This sounds very similar to the versioning supported by Hibernate Envers. You might want to look at that and incorporate it into your design instead of trying to make your own versioning scheme.
How do you define a field, eg email as having an index using JPA annotations. We need a non-unique key on email because there are literally millions of queries on this field per day, and its a bit slow without the key.
#Entity
#Table(name="person",
uniqueConstraints=#UniqueConstraint(columnNames={"code", "uid"}))
public class Person {
// Unique on code and uid
public String code;
public String uid;
public String username;
public String name;
public String email;
}
I have seen a hibernate specific annotation but I am trying to avoid vendor specific solutions as we are still deciding between hibernate and datanucleus.
UPDATE:
As of JPA 2.1, you can do this. See: The annotation #Index is disallowed for this location
With JPA 2.1 you should be able to do it.
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Index;
import javax.persistence.Table;
#Entity
#Table(name = "region",
indexes = {#Index(name = "my_index_name", columnList="iso_code", unique = true),
#Index(name = "my_index_name2", columnList="name", unique = false)})
public class Region{
#Column(name = "iso_code", nullable = false)
private String isoCode;
#Column(name = "name", nullable = false)
private String name;
}
Update: If you ever need to create and index with two or more columns you may use commas. For example:
#Entity
#Table(name = "company__activity",
indexes = {#Index(name = "i_company_activity", columnList = "activity_id,company_id")})
public class CompanyActivity{
A unique hand-picked collection of Index annotations
= Specifications =
JPA 2.1+: javax.persistence.Index (or see JSR-000338 PDF, p. 452, item 11.1.23)
The JPA #Index annotation can only be used as part of another annotation like #Table, #SecondaryTable, etc.:
#Table(indexes = { #Index(...) })
JDO 2.1+: javax.jdo.annotations.Index
= ORM Frameworks =
♥ Hibernate ORM: org.hibernate.annotations.Index;
OpenJPA: org.apache.openjpa.persistence.jdbc.Index and org.apache.openjpa.persistence.jdbc.ElementIndex (see Reference Guide);
EclipseLink: org.eclipse.persistence.annotations.Index;
DataNucleus: org.datanucleus.api.jpa.annotations.Index;
Carbonado (GitHub): com.amazon.carbonado.Index;
EBean: com.avaje.ebean.annotation.Index or io.ebean.annotation.Index ?
Ujorm: Annotation org.ujorm.orm.annot.Column, index and uniqueIndex properties;
requery (GitHub. Java, Kotlin, Android): Annotation io.requery.Index;
Exposed (Kotlin SQL Library): org.jetbrains.exposed.sql.Index, org.jetbrains.exposed.sql.Table#index(). Example:
object Persons : IdTable() {
val code = varchar("code", 50).index()
}
= ORM for Android =
♥ ActiveAndroid: Annotation com.activeandroid.annotation.Column has index, indexGroups, unique, and uniqueGroups properties;
UPDATE [2018]: ActiveAndroid was a nice ORM 4 years ago, but unfortunately, the author of the library stopped maintaining it, so someone forked, fixed bugs, and rebranded it as ReActiveAndroid - use this if you're starting a new project or refer to Migration Guide if you want to replace ActiveAndroid in a legacy project.
ReActiveAndroid: Annotation com.reactiveandroid.annotation.Column has index, indexGroups, unique, and uniqueGroups properties;
ORMLite: Annotation com.j256.ormlite.field.DatabaseField has an index property;
greenDAO: org.greenrobot.greendao.annotation.Index;
ORMAN (GitHub): org.orman.mapper.annotation.Index;
★ DBFlow (GitHub): com.raizlabs.android.dbflow.sql.index.Index (example of usage);
other (lots of ORM libraries at the Android Arsenal).
= Other (difficult to categorize) =
Realm - Alternative DB for iOS / Android: Annotation io.realm.annotations.Index;
Empire-db - a lightweight yet powerful relational DB abstraction layer based on JDBC. It has no schema definition through annotations;
Kotlin NoSQL (GitHub) - a reactive and type-safe DSL for working with NoSQL databases (PoC): ???
Slick - Reactive Functional Relational Mapping for Scala. It has no schema definition through annotations.
Just go for one of them.
JPA 2.1 (finally) adds support for indexes and foreign keys! See this blog for details. JPA 2.1 is a part of Java EE 7, which is out .
If you like living on the edge, you can get the latest snapshot for eclipselink from their maven repository (groupId:org.eclipse.persistence, artifactId:eclipselink, version:2.5.0-SNAPSHOT). For just the JPA annotations (which should work with any provider once they support 2.1) use artifactID:javax.persistence, version:2.1.0-SNAPSHOT.
I'm using it for a project which won't be finished until after its release, and I haven't noticed any horrible problems (although I'm not doing anything too complex with it).
UPDATE (26 Sep 2013): Nowadays release and release candidate versions of eclipselink are available in the central (main) repository, so you no longer have to add the eclipselink repository in Maven projects. The latest release version is 2.5.0 but 2.5.1-RC3 is also present. I'd switch over to 2.5.1 ASAP because of issues with the 2.5.0 release (the modelgen stuff doesn't work).
In JPA 2.1 you need to do the following
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Index;
import javax.persistence.Table;
#Entity(name="TEST_PERSON")
#Table(
name="TEST_PERSON",
indexes = {
#Index(name = "PERSON_INDX_0", columnList = "age"),
#Index(name = "PERSON_INDX_1", columnList = "fName"),
#Index(name = "PERSON_INDX_1", columnList = "sName") })
public class TestPerson {
#Column(name = "age", nullable = false)
private int age;
#Column(name = "fName", nullable = false)
private String firstName;
#Column(name = "sName", nullable = false)
private String secondName;
#Id
private long id;
public TestPerson() {
}
}
In the above example the table TEST_PERSON will have 3 indexes:
unique index on the primary key ID
index on AGE
compound index on FNAME, SNAME
Note 1: You get the compound index by having two #Index annotations with the same name
Note 2: You specify the column name in the columnList not the fieldName
I'd really like to be able to specify database indexes in a standardized way but, sadly, this is not part of the JPA specification (maybe because DDL generation support is not required by the JPA specification, which is a kind of road block for such a feature).
So you'll have to rely on a provider specific extension for that. Hibernate, OpenJPA and EclipseLink clearly do offer such an extension. I can't confirm for DataNucleus but since indexes definition is part of JDO, I guess it does.
I really hope index support will get standardized in next versions of the specification and thus somehow disagree with other answers, I don't see any good reason to not include such a thing in JPA (especially since the database is not always under your control) for optimal DDL generation support.
By the way, I suggest downloading the JPA 2.0 spec.
As far as I know, there isn't a cross-JPA-Provider way to specify indexes. However, you can always create them by hand directly in the database, most databases will pick them up automatically during query planning.
EclipseLink provided an annotation (e.g. #Index) to define an index on columns. There is an example of its use. Part of the example is included...
The firstName and lastName fields are indexed, together and individually.
#Entity
#Index(name="EMP_NAME_INDEX", columnNames={"F_NAME","L_NAME"}) // Columns indexed together
public class Employee{
#Id
private long id;
#Index // F_NAME column indexed
#Column(name="F_NAME")
private String firstName;
#Index // L_NAME column indexed
#Column(name="L_NAME")
private String lastName;
...
}
OpenJPA allows you to specify non-standard annotation to define index on property.
Details are here.
To sum up the other answers:
Hibernate: org.hibernate.annotations.Index
OpenJPA: org.apache.openjpa.persistence.jdbc.Index
EclipseLink: org.eclipse.persistence.annotations.Index
I would just go for one of them. It will come with JPA 2.1 anyway and should not be too hard to change in the case that you really want to switch your JPA provider.
It's not possible to do that using JPA annotation. And this make sense: where a UniqueConstraint clearly define a business rules, an index is just a way to make search faster. So this should really be done by a DBA.
This solution is for EclipseLink 2.5, and it works (tested):
#Table(indexes = {#Index(columnList="mycol1"), #Index(columnList="mycol2")})
#Entity
public class myclass implements Serializable{
private String mycol1;
private String mycol2;
}
This assumes ascendant order.