I'm relatively new to Grails.
I have the following
class House {
Integer number
Integer maxResidents
static belongsTo = [town: Town]
}
class Town {
String name
static hasMany = [houses: House]
}
I want to get five towns with most Houses. I have seen the possibility to create a criteria but I can't deal with it now. Can someone support?
Thank you!
As you have a bidirectional association you can do this with a query on House:
def result = House.withCriteria {
projections {
groupProperty("town", "town")
rowCount("numHouses")
}
order("numHouses", "desc")
maxResults(5)
}
This would return you a list of results where each result res has the town as res[0] and the number of houses as res[1]. If you'd prefer each result to be a map giving access to res.town and res.numHouses then you should add
resultTransformer(AliasToEntityMapResultTransformer.INSTANCE)
after the maxResults line (along with the appropriate import at the top of your file).
Related
I am creating a basic CRUD application with a Person entity:
class Person {
public int Age;
...
public int getAge() {
return this.Age;
}
public void setAge(int AgeToSet) {
this.Age = AgeToSet;
}
}
I have a controller and I want to retrieve all Persons with an age of 20:
def filter = {
def c = Person.createCriteria();
def persons = c.list{
eqProperty("Age", "20");
}
[persons: persons];
}
But this is not working and is, instead, giving me the error:
ERROR StackTrace - Full Stack Trace:
org.hibernate.QueryException: could not resolve property: Age of: project.Person
at org.hibernate.persister.entity.AbstractPropertyMapping.propertyException(AbstractPropertyMapping.java:62)
What could be the problem?
Three things:
Your Age needs to start with lowercase: age.
Your criteria is wrong, you want to use eq. eqProperty compares two properties, but you only need one and a value.
Your comparision must be with an int, like this: eq("myage", 20).
Since this query is so simple, you may want to just use a DynamicFinder: http://gorm.grails.org/6.0.x/hibernate/manual/index.html#finders
With a Dynamic Finder, you could simplify the query to:
def persons = Person.findAllByAge(20)
Just a suggestion. I use Dynamic Finders as my primary query method. If I need a query that is more complex, I'll resort to a .createCriteria and then a .executeQuery which takes HQL.
I need to do simple search (Two my example-simple domains and controller action are below). I want to return list of users with firstName, lastName or Car.carName like searchPattern
class User {
String firstName
String lastName
static hasMany = [car : Car]
}
class Car {
User user
String carName
}
def list(String search){
...
def searchPattern = "%" + search + "%"
def domains = User.createCriteria().list(max: max, offset: offset) {
or {
like("firstName", searchPattern)
like("lastName", searchPattern)
car {
like("carName", searchPattern)
}
}
}
It returns incorrect results - doesn't see user, which hasn't got car. Can you help me to change it for correct working? Thanks a lot
try this one:
car{
or{
isNull 'carName'
like 'carName', searchPattern
}
}
First you need to set up the domain class associations correctly. It seems you're going for a has-many association between User and Car. There are two variations: uni-directional and bi-directional. However, your implementation uses neither. Going with the assumption that you want a bi-directional association, you'll need to modify your Car class like this:
class Car {
static belongsTo = [user: User]
String carName
}
And for clarity, since a User has many Cars, it'd be worth pluralizing the collection name:
class User {
String firstName
String lastName
static hasMany = [cars : Car]
}
For more on associations, you can read my article on the subject.
Next, since you want Users even if they do not have Cars, you should know about a subtle default built into GORM: the SQL database tables are automatically INNER JOINed. It is this INNER JOIN that's causing Users without Cars to be ignored. To address this, you'll need to change the join to an OUTER JOIN. You can do something like this:
import static org.hibernate.sql.JoinType.*
def domains = User.createCriteria().list(max: max, offset: offset) {
createAlias('cars', 'c', LEFT_OUTER_JOIN)
or {
like("firstName", searchPattern)
like("lastName", searchPattern)
like("c.carName", searchPattern)
isNull("c.carName")
}
}
If I recall, aliases are used differently, hence the c.carName. You can read a bit more about using a LEFT OUTER JOIN here.
Thanks a lot to all for your help and for usefull links. This decided my problem:
import org.hibernate.criterion.CriteriaSpecification
.....
def domains = User.createCriteria().list(max: max, offset: offset) {
createAlias('cars', 'c', CriteriaSpecification.LEFT_JOIN)
or {
like("firstName", searchPattern)
like("lastName", searchPattern)
like("c.carName", searchPattern)
}
I am using Grails 2.2.4 and having one Domain contains value as map and I want to find domain object using key of map. Please help me to resolve this issue.
Student.groovy
package com.grails
import java.util.Map;
class Student {
String firstName
String lastName
Map address
static constraints = {
}
}
When My application are run I can see that Grails application create tables in database are as follow:
1) first table
student
id
version
first_name
last_name
indexes
2) second table
student_address
address
addres_idx
addres_elt
When I save Domain as:
def std = new Student()
std.firstName = 'Piyush'
std.lastName = 'Chaudhari'
std.address = [city:'Surat',state:'Gujarat',pincode:'38001']
std.save(flash:true)
values are insert in database as follow:
student table
ID VERSION FIRST_NAME LAST_NAME
1 0 Piyush Chaudhari
student_address table
ADDRESS ADDRESS_IDX ADDRESS_ELT
1 city Surat
1 state Gujarat
1 pincode 38001
Now, I want data or row using GORM like Student.findBy_____ or Student.findAllBy______
where 'city' = surat
Any one can help me to resolved this issue?
You can use:
Student.findBy<FieldName1>And<FieldName2> (<FieldNameParameter1>, <FieldNameParameter2>)
Or Either:`
Student.list().find { it.address.city == 'Surat' }
Student.list().findAll { it.address.city == 'Surat' }
`
I don't think that you can search things like this using maps.
Maybe you can do this:
def students = Student.list()
def result = students.each { student -> student.address.city == 'Surat' }
println("Resultado" + result)
But this is a very bad way to do this kind of things
Define an address class, and then add an address field to the student class (this will change how your tables are mapped in the database):
class Student {
String firstName
String lastName
Address address
static constraints = {
}
}
class Address {
String city
String state
String pincode
}
Address should be another entity in your domain, not a map of values. Remember that Grails GROM is an ORM, so you should design your domain using a OOP model in order to take advantage of the dynamic finders and criterias for doing queries.
With those changes in place, you can now use a simple criteria:
def students = Student.withCriteria{
'address'{
eq('city', 'surat')
}
}
More information about criterias in the grails docs:
http://grails.org/doc/latest/ref/Domain%20Classes/withCriteria.html
http://grails.org/doc/latest/guide/single.html#criteria
If you want to use Dynamic finders, you will have to get all the address with city = 'surat' and then use a findByAddressInList(...). But i think that in this case, criterias is a better approach
I ran into some problems while trying to count items.
Imagine the following domain classes
class Book {
String name
}
class Author {
String name
static hasMany = [books:Book]
}
How do I get a list of Authors sorted by number of Books?
here's my try:
def c = Author.createCriteris()
c.list {
projections {
count 'books', 'numBooks'
groupProperty 'id'
}
order 'numBooks', 'desc'
}
but somehow I get only unusable results... and I don't know how to join the Author objects to the rsult list.... :-(
Havent tried it, but couldn't you do something like:
class Author {
String name
static hasMany = [books:Book]
static namedQueries = {
sortByMostBooks {
books {
order('size', 'desc')
}
}
}
}
And then get access by the cleaner named query
Author.sortByMostBooks.list();
In addition, you may want to include a belongsTo in you Book domain class:
static belongsTo = Author;
or:
static belongsTo = [authors:Author];
if a book is likely to have multiple authors
got something!
I still don't know how to do it with a criteria, but by switching to HQL, I succeeded.
So if someone comes up with a criteria solution, he will still get the bonus for the correct answer :-)
here is my query:
Author.executeQuery("""
select
a, size(a.books) as numBooks
from
Author a
group by
id
order by
numBooks DESC
""",[max:20])
This query isn't efficient, since it fetches all Authors in a loop, but that's ok for now.
Grails 1.1.1
Goovy 1.5.7
In a relationship such this:
Author 1 -- n Book n -- 1 Publisher
Defined in Grails:
class Author {
String firstName
String lastName
static hasMany = [books: Book]
static constraints = {
books(nullable: true)
}
}
class Book {
String title
Author author
Publisher publisher
static constraints = {
author(nullable: true)
publisher(nullable: true)
}
}
class Publisher {
String name
static hasMany = [books: Book]
static constraints = {
books(nullable: true)
}
}
I want to load a Book with the values of Publisher and Author.
When i get a Book with the query:
def book2 = Book.findAllByAuthor(author)
I get the response with the autor assosiated but the publisher only have the id and name class in the other query:
def book3 = Book.findAllByPublisher(publisher)
I retrieve me the inverse result,i have the book with the publisher data but the author only have the id and the class name.
Where is the error in the defined model ? o there is an error in the way to do the queries ?
Edit:
I need the way to retrieve the values only with the query like this:
def book2 = Book.findAllByAuthor(author, [fetch:[publisher:'eager']])
In this one I can manage the value of publisher.
Question: If publisher had a hasmany or Domain related, getting the book I'm able to read the attributes?
Thanks.
Thanks.
Lazy fetching is used by default with gorm associations. If you want to enable eager fetching, you can modify the ORM DSL by adding the following mappings block to your Author domain class:
static mapping = {
books lazy:false
}
or you could change the fetch mode in the domain object by adding following code after your books relationship is defined.
static fetchMode = [books:"eager"]
Doing the same to your Publisher domain object should allow you to accomplish what you want. You do want to be careful of the consequence that you may load more data than you intend to.
Shouldn't the get() method return what you are looking for?
Example: def book2 = Book.get(author)
You'd better use Criteria and explicitly define which relations should be loaded eagerly. Just mention relation in the query.
Example:
def c = Teacher.createCriteria()
List<Teacher> results = c.list {
subjects {
attendees {}
}
}