I am using Grails 2.2.4 to build a web application, and now I am having a complex problem with Grails withCriteria operation. I have 3 classes as below:
class Person {
int id
String name
Set<Car> cars = [] // One-to-many relationship
Company currentCompany // One-to-one relationship
}
class Car {
int id
String manufacturer
String brand
double price
Person owner
}
class Company {
int id
String name
Set<Person> employees = []
}
And now I want to query data from Person as root class along with associated data like this:
List result = Person.withCriteria {
projections {
property('id')
property('name')
createAlias('cars', 'c', CriteriaSpecification.LEFT_JOIN)
property('c.brand')
createAlias('currentCompany', 'com', CriteriaSpecification.LEFT_JOIN)
property('com.name')
}
lt('id', 10L)
resultTransformer(CriteriaSpecification.DISTINCT_ROOT_ENTITY)
}
And the problem is, I don't know how to transform deeply the result data to a List of persons to make sure every single element contains its data as the class structure. I tried many methods like
resultTransformer(CriteriaSpecification.DISTINCT_ROOT_ENTITY)
resultTransformer(CriteriaSpecification.ALIAS_TO_ENTITY_MAP)
resultTransformer(CriteriaSpecification.aliasToBean(Person.class))
but nothing worked as I expected.
Does Grails 2.2.4 support this? If yes so what is the correct syntax?
Thank you so much.
Actually, after researching many articles, Grails documentation and even its source code, I think the best way to do this is implementing a custom transformer for my own purpose. The most difficult thing here is how to transform data to association objects and gather them to collection inside the root entity. And I have created one here:
http://www.mycodestock.com/code/10333/
Hope it helps you guys who may need something like mine.
Related
I'm trying to build a hierarchy of a class I've called group. The domain is fairly simple:
class SubGroup implements Serializable {
Group child
Group parent
static mapping = {
id composite: ['child', 'parent']
}
}
class Group implements Serializable {
int groupId
String key
String title
static mapping = {
id name: 'groupId'
}
}
Basically I'd like to build up a map of group parents and their associated children. So I'm looping through each record (if there's a cleaner way to query for a Map I'm happy to hear it) and creating the map entry for it.
Map hierarchy = [:]
SubGroup.list().each { relation ->
if (!hierarchy[relation.parent]) {
hierarchy[relation.parent] = new HashSet()
}
hierarchy[relation.parent] << relation.child
}
I would think hibernate would use some simple query that does this something like this:
select * from sub_group s, group c, group p
where s.child_id = c.group_id and s.parent_id = p.group_id
But it is not doing the join. It is doing a query of the subgroup followed by n queries of the group table (N+1 select problem). Ugh. I heard in 2.0 there's a problem with the hibernate query cache so I disabled it. I've tried adding lazy: false, and fetch: join to my SubGroup domain class for both the parent and the child columns with no luck. I've tried adding (fetch: [child: 'eager']) as a parameter to the list method. It will not do the join. Am I missing something? To be honest, it shouldn't really even need to do a join as I am only accessing the groupId foreign key property although later on I will need both the key and title properties.
I could, of course, make the child and parent properties ints and just do my own querying when I need the rest of the data or I could use HQL and some other method for limiting this to a single query, but it seems like GORM should be doing this for me. Thanks for your help.
Regards,
Jim
It seems the only way I could get this to work without hibernate making a select call for each child and parent was to instead do a HQL query rather than using the list method as shown below:
Map hierarchy = [:]
def subGroups = SubGroup.executeQuery("SELECT s.parent, s.child FROM SubGroup s")
subGroups.each { relation ->
if (!hierarchy[relation[0]]) {
hierarchy[relation[0]] = new HashSet()
}
hierarchy[relation[0]] << relation[1]
}
Thus I'm really only using the SubGroup domain class to define the relationships. I would think I should be able to do this via some kind of mapping but I couldn't figure out how.
UPDATED
I have a domain classes as below
class Training{
// has one createdBy object references User domain and
// has one course object references Course domain
// has One Trainer1 and Trainer2 objects refernces Trainer Object.
}
class Trainer{
String name
//can have many trainings.
//If Trainer gets deleted, the trainings of him must be deleted
}
Class User{
String name
// can have many trainings.
}
class Course{
String name
//If Course gets deleted, Trainings of this course must be deleted
// can have many trainings.
}
I have got a training create page, Where I have to populate already saved Course, User, Trainer1 and Trainer2. I am not saving them while Creating the training.
So, How to specify the relationship in grails
You did not put any effort to searching answer for yourslef. There are plenty basic examples and blog posts how to map relations in Grails. You should start with Grails documentation of GORM - Grails' object relational mapping. You can find it here.
I see some minor flaws in yout initial design: ie why should training be deleted if user is deleted when trainings will obviously tie with many users. Can training exists without trainers or vice versa ?
I would start with something like this:
Class Training {
static hasMany = [users: User, trainers: Trainer]
static belongsTo = Course
}
Class Trainer {
String name
}
Class User {
String name
}
Class Course {
String name
static hasMany = [trainings: Training]
}
EDIT: I have to agree with Tomasz, you have jumped here too early without searching for answers yourself. Grails.org has good documentation about GORM with examples too.
I'm having difficulties retrieving relationships when the relationship type is annotated with a #RelationshipType field.
The relationships look correct in Neoclipse, but I'm retrieving no results in my application.
The code that doesn't work is (simplified):
#NodeEntity
public abstract class Entity {
#RelatedToVia
private Collection<Relationship> relationships;
public Relationship relatedTo(Entity entity, String type) {
Relationship relationship = new Relationship(type, this, entity);
relationships.add(relationship);
return relationship;
}
...
}
and:
#RelationshipEntity
public class Relationship {
#RelationshipType
private String type;
...
}
The code that does work is:
#RelationshipEntity(type = "something")
public class Relationship {
...
}
However, this doesn't suit my use case (I have a bunch of different Relationship types between arbitrary combinations of Entity instances.
The full test code is below. Agency and Item are both subclasses of Entity.
// Create first entity
Agency arnz = agencyRepository.save(new Agency());
arnz.setCode("ARNZ");
agencyRepository.save(arnz);
// Create second entity
Item r123 = itemRepository.save(new Item());
r123.setCode("R123");
// Create parent/child relationship between entities
r123.relatedTo(arnz, EntityRelationshipType.PARENT);
itemRepository.save(r123);
// Retrieve entity from database
Entity entity = itemRepository.findByCode("R123");
// Verify that relationship is present
assertThat(entity.getRelationships().iterator().hasNext(), is(true));
The final line is where the test is failing. Any clues?
M
PS. I'm a rank amateur with Neo4j and just happened to find #RelationshipType, so I may well be doing something laughably wrong. I hope so!
Sorry to disappoint you, but during the retrieval the code right now doesn't look for the type class but rather for the type from #RelatedToVia or #RelationshipEntity or the field name relationships as relationship-type. But you're making a valid point, can you please raise in issue in JIRA?
Did you look into template.getRelationshipsBetween ?
Why don't you create individual classes for your relationships? What is the use-case for this approach?
Imagine i have the following (this is a search mechanism for my website)
class Supermarket {
String sp_name
String sp_street
}
class Products {
String p_name
String p_price
}
class products_supermarket{
Supermarket sp
Products pro
}
Now i want to create a criteria:
def c = Supermarket.createCriteria()
def results = c.list {
like("sp_street", params.street)
and {
************ ... params.product
}
maxResults(10)
}
Where i have the * i want to be able to find products whithin that supermaked searching on products_supermarket class. How to do that?
PS. If criteria works as an each() method, iterating over all supermarkets, i could use an if-else statment to search for products, and if found i could use: idEq(it), where it is the supermarket id. This way i would make it. My problem is, i dont know how to get current'sm supermarket id. Any help?
and is applied to criterias inside it, so there's no point applying it to a single statement. Top-level criterias are and-ed by defauilt.
You usually better go without connector class, just by using hasMany: Supermarket and hasMany: Product in domain classes. Connector table will be auto-generated by Hibernate.
If you stick with ProductsSupermarket connector class, do add belongsTo: Supermarket and belongsTo: Product to it class, and add 'hasMany: ProductsSupermarket' to other two, or you're losing Grails' GORM advantage.
There's a section "Querying Associations" in the doc.
Object's id is as simple as that: mySupermarket.id, or mySupermarket.ident() if key field is named differently. id field is auto-added to class and table by default.
So the query is:
List<Supermarket> results = Supermarket.withCriteria {
like("sp_street", params.street)
productSupermarket {
product {
idEq(params.product)
}
// or just eq('product', someProduct)
}
************ ... params.product
maxResults(10)
}
Let's say I have two tables employee and salary with a 1:N relationship (one salary can be associated with many employees).
In plain SQL the tables would be joined with:
SELECT e.id, e.name, s.salary FROM employee e, salary s WHERE s.id = e.salary_id AND e.id = 12345;
Assuming the following GORM-powered domain class how do I map the legacy database structure to the class?
class Employee {
String name
int salary
}
Clarification #1: I want only one domain class containing data from both tables. Adding another class is hence not an option.
Clarification #2: The question I'm trying to find an answer to is simply "how do I map two tables to one class using Grails/GORM"? If you believe that it is impossible to do so, then please state that clearly in your answer rather than trying to restate the question.
IMO it is not possible with plain Grails/GORM to join multiple tables and map them to one Domain class. As a workaround you could use a legacy XML hibernate mapping and leverage the join feature to achieve your desired goal. Of course you would loose a lot of the GORM goodies.
Your SQL example indicates there are two tables, Employee and Salary. This should also be reflected in your classes. So instead of one, you need two classes. The GORM mapping would then look like this.
class Employee {
String name
Salary salary
}
class Salary {
static hasMany = [ employees : Employee ]
int salary
}
See http://www.grails.org/GORM+-+Defining+relationships
You could, instead of having salary and name as properties, have them as get* methods that actually run a query on both these tables.
granted, that isnt the grails way, and its strongly recommended that you do follow the grails way.
I don't fully understand the limitation on not being able to add another class if there are 2 tables in the database, but if you're looking to have a unified interface, would it work to delegate the methods to the Salary class?
Something like:
class Salary {
int amount
}
class Employee {
Salary _salary
String name
String toString() { name }
public Integer getSalary() {
return _salary?.amount
}
public void setSalary(Integer amount) {
// not quite sure of your business logic here, this is a guess
_salary = Salary.findByAmount(amount)
if (!_salary) {
_salary = new Salary(amount: amount)
_salary.save()
}
}
}
def e = new Employee(name:"willy loman", salary: 100)
e.save()
assert e.salary == 100
It's also possible that you might be able to make what you're asking for work with a custom hibernate mapping file, but I'm not familiar enough with contorting hibernate in that manner to say for sure.
See the Custom User Type section of this page.