I have problem which is easy to solve with pure SQL but I need to solve it with Doctrine in YAML.
I have well known db tables users and friends. Where users table has primary key user_id and friends has friend_id and friend_with_id which uses user_id from table user. My problem starts when I need to add there one more column mood. With SQL I add to table friends onemore column named mood and it's done with doctrine I can't find any solution.
For better understanding I add db scheme:
I dont see any self-reference relationship here. Both friend_id and friend_with_id points to users.user_id. What I see is, two one-to-many relationships from the user side OR two many-to-one relationships from the friends side.
So, there will be two ArrayCollection objects (ManyToOne) in the Friend entity corresponding to friend_id and friends_with_id. Similarly two ArrayCollections (OneToMany) on the User entity, namely, myFriends and friendsWith.
Related
I'm having some problems with the following...
I have a table with phone numbers. I want to use the same table for both users and companies. A user can have several phone numbers and a company too. So i want a One to many unidirectional relationship with two different join tables. One linking phone numbers to users, the other linking phone numbers to companies.
This is solution following the doctrine2 manual chapter 5.9 found here: (click)
My users entity holds this code:
/** #ORM\ManyToMany(targetEntity="Application\Entity\PhoneNumber")
* #ORM\JoinTable(name="user_phone_number_linker",
* joinColumns={#ORM\JoinColumn(name="user_id", referencedColumnName="id")},
* inverseJoinColumns={#ORM\JoinColumn(name="phone_number_id", referencedColumnName="id")}
* )
*/
protected $phone_numbers;
I use a unidirectional one to many because the thing is I can't make a bidirectional one because if I refer back to the user I cannot use the same phone number entity class for the company. Now it all works fine, but when I delete a phone number I get the following error:
An exception occurred while executing 'DELETE FROM phone_number WHERE id = ?' with params {"1":1}:
SQLSTATE[23000]: Integrity constraint violation: 1451 Cannot delete or update a parent row: a foreign key constraint fails (database/user_phone_number_linker, CONSTRAINT user_phone_number_linker_ibfk_11 FOREIGN KEY (phone_number_id) REFERENCES phone_number (id))
If I set the ON DELETE CASCADE value manually in the database it works fine, but this is not the idea of using doctrine2 and I think I should be able to solve it within the code without going to my phpMyAdmin panel. Somehow the cascading from the phone number towards the join table should be initiated on deletion, but without making a reference back to the join table from the phone_number entity.
Hope someone smart can help me solve this.
EDIT
In the meantime I learned a lot more about Doctrine2 and reviewing my old question made me realize that this is not a correct way to store several phoneNumbers in one table in the first place. To be able to store user phone numbers and company phone numbers in the same table I should use table inheritance with a discriminator column. The column should hold some user/company discriminator.
Because of this column the doctrine ORM will "know" if that phoneNumber is actually a user or a company phone-number. I need to make two different entity definitions following the single table inheritance mapping principles from the doctrine 2 specs.
One class UserPhoneNumber will have a many-to-one relationship with User the other called CompanyPhoneNumber a one-to-many relationship with Company. I don't necessarily need a join column, the user_id or company_id columns can be in the phone-number table. In the User class the Company association is omitted and in the Company class the User association is omitted (database should allow null values for those columns).
If I do use a join table it is according to the one-to-many unidirectional with join table description in the Doctrine2 specs
READ MORE
Otherwise you can also read more on associations and cascade issues here on this elaborate Doctrine2 in depth website.
As you said, your relation is unidirectional. You've defined a relation from Users to PhoneNumbers. The cascade delete will work when you delete a User, it will remove all rows in user_phone_number_linker because that's the relation you've defined.
If you want to do it the other way, you've got to create a relation from PhoneNumbers to Users. Doctrine needs it to work for you. But you have the problem that the entity is shared by two other entities, Users and Companies.
Keep in mind that entities are objects, not tables. So you could try to create two entities to the same table, one named PhoneNumberUsers and the other PhoneNumberCompanies. This way you'll be able to create the needed relation to do the cascade delete. I haven't tested by myself, but I think it could work.
By the way, you can remove the oncascade parameter on the Users' entity join table. I've the same scenario as you with users and roles, and I haven't used it. I think it's only needed when you want to cascade from entity to entity. I'm not sure about that, but that's what I've been experiencing until now.
My bad,
The phone number user relationship is regarded a Many-To-Many relationship, so if want to remover the phone number I should not only remove the phone number itself, but I have to explicitly remove the phone number from the user as well. So in the Controller like this:
// Remove the phone number user connection from the database
$user->removePhoneNumber($phone_number);
// Remove the phone number from the database
$em->remove($phone_number);
I just thought the unique restriction which makes the relationship to a unidirectional One-To-Many would be enough to make doctrine take care of it. That was not correct.
I am trying to implement some tables that mimic inheritance in a relational (sqlite) database. My goal is to have one master table with general fields, and some child tables with specialized fields. Every record in the master table will have exactly one counterpart in exactly one of the specific tables. What I want looks like this:
Master table:
id (PK) #Your average web2py unique auto-incrementing int field
#Some general fields
Child tables:
id (PK, FK referencing the PK of the master table)
#Some specialized fields
Having a default "id" PK for each child table has no use to me. All I need is an FK reference to the master table, which can serve as the PK for the child tables. This means that the PK of the child tables will be unique, but will contain gaps. This is because a child table will only reference some of the records of the master table.
I get the impression that doing this (not giving the child tables the regular "id" PK) is against the Web2py way. So my questions are as follows:
Is this a Bad Idea™? If so, why?
How would I implement this? Can Web2py handle tables that don't have an auto-incrementing int as PK?
It's very important for me to apply the correct style and practice when writing code. I am open to alternative approaches.
Thank you for your help.
See the book section on keyed tables. If this is a database specifically for use with web2py, I suggest you stick with the standard web2py approach:
db.define_table('master', ...)
db.define_table('child', Field('master', db.master))
I'm hitting a wall here and I know this is a simple question, but I was unable to find it here.
In an ER diagram, what would the relationship be between two objects that have a ManyToMany relationship, in terms of the intermediary table?
Example:
item ---- item_facts ---- fact
I feel like it should be one to one but I'm not completely sure.
user --many2many-- group
user 1----n user_group n---1 group
In django documentation it states that
A many-to-many relationship. Requires a positional argument: the class to which the model is related. This works exactly the same as it does for ForeignKey, including all the options regarding recursive and lazy relationships.
Behind the scenes, Django creates an intermediary join table to represent the many-to-many relationship. By default, this table name is generated using the name of the many-to-many field and the model that contains it. Since some databases don't support table names above a certain length, these table names will be automatically truncated to 64 characters and a uniqueness hash will be used. This means you might see table names like author_books_9cdf4; this is perfectly normal. You can manually provide the name of the join table using the db_table option.
And ForeignKey definition is like:
A many-to-one relationship. Requires a positional argument: the class to which the model is related.
So,ManyToMany relations created by django are creating intermedıary tables that are 1 to N.
Not sure what the question is here. You say that the two objects have a many-to-many relationship.
If two objects (entitied, tables) have a many-to-many relationship, whether you include the intermediate table in the diagram or not, is irrelevant. They still have a many-to-many relationship.
I have three entities: User, Office and PhoneNumber. The user has many phone numbers, and the office has many phone numbers too.
The problem is how to represent these entities relations in Doctrine 2.
At first I tried to use bi-directional one-to-many associations
(User -> has many -> PhoneNumbers) (Office -> has many ->
PhoneNumbers), the PhoneNumber has two mapping fields, one for User
and anotherone for Office. This solution doesn't work since one of
the mapping foreign keys couldn't be null.
My second approach was to use two entities and one superclass for PhoneNumber. The PhoneNumber superclass has defined all common fields except the mapping field. Entities UserPhoneNumber and
OfficePhoneNumber extended the PhoneNumber entity and specified the
different mapping field and different table. (one table for OfficePhoneNumbers, anotherone for UserPhoneNumbers)
This solution actually works, but it is quite ugly to have 3
classes to represent one simple entity.
My third approach is to use uni-directional one-to-many mapping. This will eliminate the need of mapping field for the PhoneNumber entity. The problem is that when I use cascade remove for the many-to-many field, it violates the integrity constraint when deleting records.
When I omit the cascade remove option, after removing User or Office, the PhoneNumber remains in the Database (but the record in mapping table is removed).
What is the best way to handle this type of association?
Thanks
I finally solve the problem connected with (probably the nicest) solution 1). The problem was in misunderstanding of mappedBy attribute which should specify the entity field, not the database field.
I have a legacy database with a table storing a many-to-many relationship, but without a single primary key column. Is there any way to convince Django to use it anyway?
Schematically:
Product 1<---->* Labeling *<---->1 Label
The Labeling table uses (product_id,label_id) as a compound primary key, and I don't see any way to inform Django about this. (Just using through gives me Unknown column 'labeling.id' in 'field list'.)
Do I need to fall back to custom SQL? Or am I missing something?
hope this helps you,
http://docs.djangoproject.com/en/dev/ref/models/options/#unique-together
http://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.Field.db_index
If you add a unique_together to the model for the many-to-many table, Django will use those columns instead of expecting a primary key called id.