I have a domain class (let's call it security) and it needs three "one to many" relationships with another domain class (let's call it role). The three relationships are "current", "previous", and "new".
Basically I'm hoping to do something like this (in reality it's more complicated, but this will do to illustrate things):
class Security
{
static hasMany = [current: Role, previous: Role, new: Role]
Set current
Set previous
Set new
}
class Role
{
static belongsTo = [security: Security]
String name
}
Unfortunately something like this doesn't work since the Role domain class maps to only one table and that one table has only one column for the Security class' ID.
Is this possible without creating three separate Role classes and instead just map one class to multiple tables?
I'm also looking at the possibility of simply including a flag in the Role class to signal whether the role is current, previous, or new and only having one "one to many" relationship in the Security class. However, this approach is causing issues with data binding, since my HTML form would need to send two pieces of information for each role (the name property and also the type). Since these roles are listed in a HTML select statement I can only send one piece of information (the name).
If you do not depend on the belongsTo in Role (you have to remove it) you can use joinTable:
class Security {
static hasMany = [current: Role, previous: Role, next: Role]
static mapping = {
current joinTable: [name:'current']
previous joinTable: [name:'previous']
next joinTable: [name:'next']
}
}
You could use Grails mappedBy, just like below, if creating 3 fields inside the Role is not an issue:
class Security {
static hasMany = [current: Role, previous: Role, new: Role]
static mappedBy = [current: 'securityForCurrent',
previous: 'securityForPrevious', new: 'securityForNew']
}
class Role {
String name
Security securityForCurrent
Security securityForPrevious
Security securityForNew
}
Related
While migrating an existing app from Grails 2.5 to 3.1, I ran into an odd issue with a bi-directional one-to-one relationship.
Imagine a simple model with a User and Employee objects. A User represents a generic user account. Not all users are Employees but all Employees are Users. Moreover Employees have references to managers, supervisors, etc (also User instances). User is the owning side of the relationship.
class User {
Employee employee
static mappedBy = [employee: "user"]
static hasOne = [employee: Employee]
static constraints = {
employee(nullable:true)
}
}
class Employee {
User user // represents employee's own account, a bi-directional one-to-one
User supervisor // represents a supervisor
static belongsTo = [user: User]
static constraints = {
user(unique:true)
supervisor(nullable:true)
}
}
The trouble after upgrading to Grails 3 is that in the create mode, this results in supervisor_id column of employee table being generated as NOT NULL, whereas in Grails 2 it was nullable as expected (with only user_id being NOT NULL).
I tested this with Grails 3.1.12 and 3.2.0, getting the same behavior with both. Am I doing anything stupid in my domain class declarations? I've tried multiple mappings to achieve the same behavior as in Grails 2.5 without luck. In some cases I'm even getting a foreign key on both sides of the relationship...
I don't know why your code was working with previous version of Grails, but it is wrong.
When you use hasMany and belongsTo, it is not necessary to define other property in the child object, and you don't need also to use the mappedBy property on the parent, and the same with the parent (property employee at User)
Grails doesn't need anything else to know which is the bidirectional property on both classes, and the constraint user(unique : true) neither.
So your classes should look like this:
class User {
static hasOne = [employee: Employee]
static constraints = {
employee(nullable: true)
}
}
class Employee {
User supervisor // represents a supervisor
static belongsTo = [user: User]
static constraints = {
supervisor(nullable:true)
}
}
It could be nice to know how is your DB structure. But in this way all foreign keys are stored in the employee table. But of course you could navigate from both entities. If you have different structure you could map your current database with this model. See this
employee.user
user.employee
I am learning grails and I came up with a use case. In my use case, a product has many users and each user can have many roles.
Here is my product class:
class Product {
String name
String description
String vision
Date startDate
Date endDate
static hasMany = [users : User, contributors : User, watchers : User, approvers : User]
static belongsTo = User
static constraints = {
}
}
Here is my User class:
class User {
static constraints = {
}
String fullName
String email
static hasMany = [roles : Roles, products : Product]
}
Here is the Roles Enum:
public enum Roles {
PRODUCTOWNER ('ProductOwner'),
APPROVER ('Approver'),
CONTRIBUTOR ('Contributor'),
WATCHER ('Watcher')
}
My question is specifically about the association between Product and User. I want to represent the fact that a product can have many users in different roles. Also, each user can be part of multiple products with a different role in each product. Is this the right way to represent this relationship? Also, I should be able to remove and add users to products and vice versa. What this also means is that, users can keep moving between roles and can move in and out of products. In this scenario, I probably don't want cascades to happen. How do I prevent automatic cascades from happening to CRUD operations for this relationship?
Thanks.
I think rather than having roles and products in User.groovy, it will be better if you create a separate domain like UserProductRole. As you said user will have different role in different products then creating a separate domain makes more sense in business usecase and also doing queries
class UserProductRole{
Role role
static belongsTo = [user:User,product:Product]
static constraints = {
user (unique:['product','role']
}
}
You can create composite key but I generally dont perfer it because it makes querying bit difficult.
And now you need to change hasMany in User and Product like following
[userProducts:UserProductRole] rather then having users or products
I want to create a domain class as like , One user can post many orders [Bidirectional] and one order can be liked by many users [unidirectional].
I have written a domain class as shown below ,
Class User {
String userName;
List orders
static hasMany = [Order]
}
Class Order {
String orderId
String orderName
//Indicates this order belongs to only one user
static belongsTo =[owner : User ] // Bidirectional
//Indicates order can be liked by many users
static hasMany = [likedUser : User] //Unidirectional
}
But I am getting am error saying invalid schema . Any body please help...
This post looks similar to my question but I am not getting , Please help.
First, order is a reserved word in SQL. Since GORM by default creates a table with the same name as your class, you'll need to either rename your class or provide a different name to use when mapping to SQL tables.
For example:
class Order {
static mapping = {
table 'user_order'
}
// ...
}
Another problem is that Order contains two associations to User. You need to tell GORM which one of these that is the bi-directional association from User to Order. That can be achieved using mappedBy, like this:
class User {
String userName
static hasMany = [orders: Order]
static mappedBy = [orders: 'owner']
}
Hope this helps.
In my domain I have a many-to-many relationship. The problem is that GORM forces me to define owner entity but I don't think that either side "owns" the relation.
class User {
String username
String password
static hasMany = [organizations: Organization]
static belongsTo = Organization
static constraints = {
}
}
class Organization {
String name;
static hasMany = [members: User]
}
In this case I'm obviously not allowed to delete User who is in some organization (because Organization "owns" the relation). I would like to be able to delete both entities and on delete simply remove the relation (row from user_organization table). Is it possible or do I have to write this logic myself (if so, what would be the best way to implement this)?
You are allowed to delete both sides of the relationship, no matter who is the "owner". The belongsTo just applies the proper cascading so you don't have to.
In your example if you want to delete a user you first have to remove the relationship. So, in order to delete a user you do:
organization.removeFromMembers(user)
user.delete()
And if you delete an organization, since it is the "owner", you just don't need to use removeFrom*.
In Grails belongsTo allows one domain class to establish a cascading relationship with another domain class. There are two styles of relationships when using belongsTo: Reference and No Reference. Reference creates a property on the owned object while No Reference merely establishes an invisible GORM relationship.
Example parent domain-class:
class Car {
Engine engine
}
belongsTo without Reference property:
class Engine {
static belongsTo = Car
}
belongsTo with Reference property:
class Engine {
static belongsTo = [car:Car]
}
Not to hard right, however the trouble for me starts when we start using multiple belongsTo references:
belongsTo with multiple back references:
class Engine {
static belongsTo = [car:Car, user:User]
}
multiple belongsTo relationships without property references:
class Engine {
static belongsTo = [Car, User]
}
Here's the problem, how do I mix the two above styles?
Say I want a property reference for the User but not for the Car, how would I write that belongsTo call?
Any information on how to mix No Reference relationship links with Reference property in a single domain class would help.
Links:
Using Grails Object Relational Mapping (GORM)
belongsTo - grails.org
This question reposted by me on the official Grails forum
class Engine {
User user
static belongsTo = [Car, User]
}
That said, I always use the map (reference) syntax over the list (no reference) syntax because I like mine to be bi-directional.