I have these two domains Car and Driver which have many-to-many relationship. This association is defined in table tblCarsDrivers which has, not surprisingly, primary keys of both the tables BUT additionally also has another boolean field deleted. Herein lies the problem. When I find/get query on domain Car, I am fetched all related drivers irrespective of their deleted status in tblCarsDrivers, which is expected.
I need to put a clause/constraint to
exclude the deleted associations from the
list of fetched records.
PS: I tried using an association domain CarDriver in joinTable name but that seems not to work. Apparently it expects only table names, not maps.
PPS: I know its unnatural to have any other fields besides the mapping keys in mapping table but this is how I got it and it cant be changed.
Car domain is defined as such -
class Car {
Integer id
String name
static hasMany = [drivers:Driver]
static mapping = {
table 'tblCars'
version false
drivers joinTable:[name: 'tblCarsDrivers',column:'driverid',key:'carid']
}
}
Thanks!
I know its unnatural to have any other
fields besides the mapping keys in
mapping table but this is how I got it
and it cant be changed.
This is not at all unusual. If you want to store properties about the relationship, this is the obvious solution. You should reinstate your association domain CarDriver which has a deleted property in addition to a relationship to Car and Driver, and you should then be able to write a query which excludes the deleted drivers.
A comprehensive example of how to define such a mapping is provided here.
Related
I have one table called countries which has a field i.e ID with primary key and the other table is customers which has a field called primary_country. I want to join both the tables in cakephp way, but always it is taking customers.country_id which is not present in the table. I am using primary_country because the table also has alternate_country field. so i can't use country_id. Please provide me any solution so that I can fetch the country names on the basis of primary_country and alternate_country.
You'll need to modify your table object with the foreign key, as mentionned here:
https://book.cakephp.org/3.0/en/orm/associations.html
It could be something like that, in your case :
class CustomersTable extends Table
{
public function initialize(array $config)
{
$this->belongsTo('Countries')
->setForeignKey('primary_country');
}
}
But i must say that if your model is still under conception, you may want to make an third table customer_countries and make an 'hasMany' relation between 'customers' and 'countries'. Limiting records for one customer to only two countries, and ordering them between 'primary' and 'alternate' is part of you business logic.
Hi I have a simple problem.
My domain class is like this:
class Example {
long seq
hasMany = [example_array: ExampleData]
long count
}
class ExampleData {
String type
long description
static belongsTo = Example
static constraints = {
}
}
This results in 3 tables, like a many to many relation.
Why is this?
Thanks
The reason for the extra table is that you've modeled the relation only in one direction - an Example can access its ExampleData instances via the example_array Set that's added to your class bytecode because of the hasMany property, but an ExampleData instance has no way to reference its owning Example.
You added a belongsTo property, but only specified the class name. That's sufficient to configure ownership, cascaded deletes, etc. but doesn't provide a property in the class to access the Example instance.
If you change it to the other supported syntax it will work as you expected:
static belongsTo = [example: Example]
Here example will end up being the name of an Example property (and you can change it and/or example_array to any valid property name), which is basically the same as declaring
Example example
Now that both sides can access the other, the relationship is bidirectional and you no longer need the third table. That's because a 1-many is typically implemented using a foreign key in the child table, in this case in the table for ExampleData that points to the table for Example. That wasn't possible without a property in the class to wire up to that column, so the join table was necessary.
I believe that you have to map the BelongsTo, like this:
static belongsTo = [example:Example]
Hope it helps :)
From the definition of hasMany Grails will, by default, map this kind of relationship with a join table.That join table is the 3rd table you mentioned.No need to worry about that.
Well the one-to-many relationship is constructed by having additional table (i.e. Example_ExampleData) containing two columns each id fields from tables of the entities forming the relationship(i.e. Example and ExampleData).
The newly added table is child to parent tables – Example and ExampleData.
So in your case when you run your application the 3rd table gets created by Grails by default as your table relationship falls under the one-to-many relationship.
I have a following domains
User (in database called usermanagement) and
Account (in another database xyz)
Its an old system so i cannot really change the architecture of the system. I have been assigned task to implement a system that a certain users can only access certain accounts. This is a classic case of many-to-many relationship but the problem lies in the fact that these two domains are in two different databases. I googled if that was possible but i realized that it was not possible. So I now am thinking of creating a custom join table to store info on which user are allowed access to which accounts. The table can have two columns 'accountId' and 'userId'. So for this, do i have to create a new domain in grails or is there any cleaver way of doing this ?
Thanks in advance.
If you create joinTable in which DB you are going to create it and how you are going handle updates in main (Account,User) tables and ceep your join table up2date ?
I think (for this case) you don't need join table, you need handle business logic in application level.
You cane have 2 Domain classes each one pointed to different dataSource(DataBase).
http://grails.org/doc/latest/guide/conf.html#multipleDatasources
As I searched for solution of this, I did not find any sustainable solutions. I eventually narrowed down the probable solutions to two:
1. Create a domain table (only) using sql, some sort of patch and use hard-coded queries in grails to write and access data to and from the table.
2. Create a domain class like AccountUser having properties clientId and userId
I choose the 2nd option, I wrote some additional methods and created a service to return user and client instance and I am done ! Anyways, thanks guys.
If the databases are "visible" to each other (on the same server or there is a db link between them), you should be able to map the domain classes using the fully qualified table names ('schema.tablename') in the mapping closure.
psuedocode:
class User {
static mapping = {
table "usermanagement.user"
}
static hasMany = [Account:accounts]
}
class Account {
static mapping = {
table "xyz.account"
}
}
http://grails.org/doc/latest/guide/GORM.html#tableAndColumnNames
Currently I'm having some trouble, creating an unidirectional relationship in Grails.
I have a class Toilet with an Attribute Address.
This Address is a seperate class.
The Address can - theoretically - still exist, if the Toilet-Object, which the Address is associated with, gets deleted.
The toilet will stay, too, if the address gets deleted.
GORM's hasOne is not what i need, because it creates a bidirectional relation.
Defining an attribute of the type class only results in a non-persisted Address (despite it's own table) - that means, the association of the Address to the Toilet-Object doesn't exist
I'm not really familiar with these kinds of relationships, so I would really appreciate a solution or another way to accomplish my goal
Hope my problem is clear - if not comment, and I will try to add further explanations
taken from
http://grails.org/doc/1.0.x/guide/5.%20Object%20Relational%20Mapping%20(GORM).html
5.3.3 Understanding Cascading Updates and Deletes
It is critical that you understand how cascading updates and deletes work when using GORM. The key part to remember is the belongsTo setting which controls which class "owns" a relationship.
Whether it is a one-to-one, one-to-many or many-to-many if you define belongsTo updates and deletes will cascade from the owning class to its possessions (the other side of the relationship).
If you do not define belongsTo then no cascades will happen and you will have to manually save each object.
So.....if you do not use belongsTo then if you manually save each object you should not have a problem.
If the address on Toilet is a simple association without a hasOne or belongsTo mapping, then no operations will be cascaded.
That means you'll have to save the address, assign it toilet.address, and save the toilet.
Found the solution.
What I left out, was the implemenation of an interface in the Toilet class.
The problem was (as a reminder) that the relationship of the address within the toilet class wasn't saved to the database.
This was a problem of the interface itself - in this interface, getters and setters were defined and had to be implemented (the way an interface works - obviously). The problem here was, that the setter of the Address-Attribute expected the Type IAddress.
I overloaded the setter to also receive a parameter of the type Address.
With this change, the relationship between Toilet and Address is saved correctly to the database - the ID of the Address is saved in the table of the Toilet.
I think the definition of the setter is just a mistake (i have no influence on the interface), but with this workaround i can get it to work anyways
Hope this explanation helps others too.
Why not have a class which models the association ?
class ToiletAddress {
Toilet toilet
Address address
...
}
... and then simply wrap your logic into a service where you assign addresses to toilets, and delete toilets or addresses.
Using constraints you can define what kind of association it is. eg 1-1, 1-n (both sides), and n-m
static constraints = {
address unique: ['toilet']
toilet validator: {val, obj -> ... }
}
I tried setting up a simple one-to-many relation in Entity Frameworks designer.
The tables are Category (1) and Transaction (N). Here's what I did:
Add "association"
End1 = Category, multiplicity 1, navigation property=Transaction
End2 = Transaction, multiplicity Many, navigation property = Category
Building it gave me the error "No mapping specified". Ok, makes sense. So I added this mapping:
Category
Category.CategoryID = Transaction.CategoryID
But the mapping designer also automatically adds a mapping for the Transaction table, which I cannot figure out how to delete or how to setup:
Transaction
Transaction.TransactionID = ???
Leaving it empty seems most valid, but that gives me: Error 3024 "Must specify mapping for all key properties (TransactionID)"
And trying to set it to a fake int property just hoping it's a compiler bug. But that gives me errors 3002 and 3003.
I dont get what to do. Isnt Associations meant to be used this way?
I suggest creating (or importing from the database) an entity for Catagory and an entity for Transaction. Add scalar properties to each as needed. Next, right-click on your entity, click Table Mapping, and map your entity properties to the table fields. For example, for the Category entity, map CategoryID field to a CategoryID property. Do the same for the other entity. THEN create the association.
Note that associations linked by exposed foreign keys do not have any mappings.
BTW, you'll probably want to add navigation properties as well.