I have multiple models which all have a FK to the same model.
All I know is the FK how can I determine which of the models has the FK attached?
Below an example to clearify:
class ModelA(models.Model):
title = models.CharField("title", max_length=80)
class ModelB(models.Model):
fk = models.ForeignKey(ModelA)
class ModelC(models.Model):
fk = models.ForeignKey(ModelA)
How can I figure out without using a try/except on each model whether B or C has the FK?
(The FK can only be in one of them, for the record in this case I only added two models but in the real world app there are multiple possible x amount of models which have the FK to modelA)
if ModelB.objects.filter(fk=your_fk):
print "B"
else:
print "C"
if you're unsure whether this fk is present in either B or C at all, add another check:
if ModelB.objects.filter(fk=your_fk):
print "B"
elif ModelC.objects.filter(fk=your_fk):
print "C"
else:
print "none"
If as you said you have many models with foreignkeys to ModelA maybe you should consider having a field in ModelA which caches this information? It could be updated by save() method of ModelB/C/.. or by a database stored procedure.
If you're after syntactic sugar and reducing number of queries try this:
a=ModelA.objects.annotate(nb=Count('modelb'), nc=Count('modelc')).get(pd=your_fk)
if a.nb:
return 'B'
elif a.nc:
return 'C'
else:
return 'A'
(django >= v1.1)
Related
I have a model B with a Many2many field referencing model A.
Now given an id of model A, I try to get the records of B that reference it.
Is this possible with Odoo search domains? Is it possible doing some SQL query?
Example
class A(models.Model):
_name='module.a'
class B(models.Model):
_name='module.b'
a_ids = fields.Many2many('m.a')
I try to do something like
a_id = 5
filtered_b_ids = self.env['module.b'].search([(a_id,'in','a_ids')])
However, this is not a valid search in Odoo. Is there a way to let the database do the search?
So far I fetch all records of B from the database and filter them afterward:
all_b_ids = self.env['module.b'].search([])
filtered_b_ids = [b_id for b_id in b_ids if a_id in b_id.a_ids]
However, I want to avoid fetching not needed records and would like to let the database do the filtering.
You should create the equivalent Many2many field in A.
class A(models.Model):
_name='module.a'
b_ids = fields.Many2many('module.b', 'rel_a_b', 'a_id', 'b_id')
class B(models.Model):
_name='module.b'
a_ids = fields.Many2many('module.a', 'rel_a_b', 'b_id', 'a_id')
In the field definition, the second argument is the name of the association table, and the two next ones are the name of the columns referencing the records of the two models. It's explained in the official ORM documentation.
Then you just have to do my_a_record.b_ids.
If you prefer doing an SQL request because you don't want to add a python field to A, you can do so by calling self.env.cr.execute("select id from module_b b, ...").fetchall(). In your request you have to join the association table (so you need to specify a name for it and its columns, as described in my code extract, otherwise they are automatically named by Odoo and I don't know the rule).
I think it's still possible to use search domains without the field in A but it's tricky. You can try search([('a_ids','in', [a_id])]) but I'm really not sure.
class A(models.Model):
_name='module.a'
class B(models.Model):
_name='module.b'
a_ids = fields.Many2many('module.a')
Now you want to search a_id = 5
To do so simply use browse or search ORM methods i.e,
a_id = 5
filtered_b_ids = self.env['module.b'].search([(a_id,'in',self.a_ids.ids)])
or
a_id = 5
filtered_b_ids = self.env['module.a'].search([(a_id)])
I have a problem retrieving values of a column from relations in Laravel.
I have a User - Model. This model has relation to a table btw. a model named Userhobbies.
For now we have:
User ::: hasMany >>> Userhobbies
Now with User::all()->load('hobbies') I'm getting right results like
{"id":"1","username":"jdoe","first_name":"Joe","last_name":"Doe","birth":"
1992-04-11","picture_id":"f3dca65323e876026b409b9ba3d49c56","hobbies":
[{"hobby_id":"1","user_id":"1"},{"hobby_id":"2","user_id":"1"},
{"hobby_id":"3","user_id":"1"},{"hobby_id":"4","user_id":"1"}]}
As you can see Userhobbies contains only primary-key relations between hobby - table (Hobby Model) and user - table (User Model).
(Hobby model also has hasMany relation to Userhobbies)
My question now is - how to retrieve all hobby-names (from hobby - table) in my call over (after load('hobbies') ) and is it possible without writting a lot of code?
For better understanding of my idea the result which I want to retrieve:
{"id":"1","username":"jdoe","first_name":"Joe","last_name":"Doe","birth":"
1992-04-11","picture_id":"f3dca65323e876026b409b9ba3d49c56","hobbies":
["golf", "cards", "games", "football"]}
EDIT:
If I try following (I tried with belongsToMany in User and Hobby):
User::with('hobbies')->get()->first()
And I'm getting the whole values from the hobbies - table:
{user-specific data ...
hobbies:[{"id":"1","name":"golf","created_at":"2015-04-07
14:15:02","updated_at":"2015-04-07 14:15:02","pivot":
{"user_id":"1","hobby_id":"1"}},
{"id":"2","name":"cards","created_at":"2015-04-07
14:15:02","updated_at":"2015-04-07 14:15:02","pivot":
{"user_id":"1","hobby_id":"2"}},
{"id":"3","name":"games","created_at":"2015-04-07
14:15:02","updated_at":"2015-04-07 14:15:02","pivot":
{"user_id":"1","hobby_id":"3"}},
{"id":"4","name":"football","created_at":"2015-04-07
14:15:02","updated_at":"2015-04-07 14:15:02","pivot":
{"user_id":"1","hobby_id":"4"}}]}
Same try with ->load('hobbies'). I really don't know how to go on.
To explain it a bit more what I need one could imagine such query as follows:
User::all(['id', 'name'])->load(array('hobbies.id','hobbies.name'))->get();
From my knowledge, I know that it's possible to use a closure to set constraints on the query that performs the load, like so:
User::all()->load(['hobbies' => function($query)
{
$query->select('id', 'name');
}]);
By doing it, when you cast it to array, it will produce a result near to what you want. You can even add 'pivot' to your $hidden property on your Hobby model to hide this information.
An NDB model contains two properties: email and password. How to avoid adding to the database two records with the same email? NDB doesn't have UNIQUE option for a property, like relational databases do.
Checking that new email is not in the database before adding—won't satisfy me, because two parallel processes can both simultaneously do the checking and each add the same email.
I'm not sure that transactions can help here, I am under this impression after reading some of the manuals. Maybe the synchronous transactions? Does it mean one at a time?
Create the key of the entity by email, then use get_or_insert to check if exists.
Also read about keys , entities. and models
#ADD
key_a = ndb.Key(Person, email);
person = Person(key=key_a)
person.put()
#Insert unique
a = Person.get_or_insert(email)
or if you want to just check
#ADD
key_a = ndb.Key(Person, email);
person = Person(key=key_a)
person.put()
#Check if it's added
new_key_a =ndb.Key(Person, email);
a = new_key_a.get()
if a is not None:
return
Take care. Changing email will be really difficult (need to create new entry and copy all entries to new parent).
For that thing maybe you need to store the email, in another entity and have the User be the parent of that.
Another way is to use Transactions and check the email property. Transaction's work in the way: First that commits is the First that wins. A concept which means that if 2 users check for email only the first (lucky) one will succeed, thus your data will be consistent.
Maybe you are looking for the webapp2-authentication module, that can handle this for you. It can be imported like this import webapp2_extras.appengine.auth.models. Look here for a complete example.
I also ran into this problem, and the solution above didn't solve my problem:
making it a key was unacceptable in my case (i need the property to be changeable in the future)
using transactions on the email property doesn't work AFAIK (you can't do queries on non-key names inside transactions, so you can't check whether the e-mail already exists).
I ended up creating a separate model with no properties, and the unique property (email address) as the key name. In the main model, I store a reference to the email model (instead of storing the email as a string). Then, I can make 'change_email' a transaction that checks for uniqueness by looking up the email by key.
This is something that I've come across as well and I settled on a variation of #Remko's solution. My main issue with checking for an existing entity with the given email is a potential race condition like op stated. I added a separate model that uses an email address as the key and has a property that holds a token. By using get_or_insert, the returned entities token can be checked against the token passed in and if they match then the model was inserted.
import os
from google.appengine.ext import ndb
class UniqueEmail(ndb.Model):
token = ndb.StringProperty()
class User(ndb.Model):
email = ndb.KeyProperty(kind=UniqueEmail, required=True)
password = ndb.StringProperty(required=True)
def create_user(email, password):
token = os.urandom(24)
unique_email = UniqueEmail.get_or_insert(email,
token=token)
if token == unique_email.token:
# If the tokens match, that means a UniqueEmail entity
# was inserted by this process.
# Code to create User goes here.
# The tokens do not match, therefore the UniqueEmail entity
# was retrieved, so the email is already in use.
raise ValueError('That user already exists.')
I implemented a generic structure to control unique properties. This solution can be used for several kinds and properties. Besides, this solution is transparent for other developers, they use NDB methods put and delete as usual.
1) Kind UniqueCategory: a list of unique properties in order to group information. Example:
‘User.nickname’
2) Kind Unique: it contains the values of each unique property. The key is the own property value which you want to control of. I save the urlsafe of the main entity instead of the key or key.id() because is more practical and it doesn’t have problem with parent and it can be used for different kinds. Example:
parent: User.nickname
key: AVILLA
reference_urlsafe: ahdkZXZ-c3RhcnQtb3BlcmF0aW9uLWRldnINCxIEVXNlciIDMTIzDA (User key)
3) Kind User: for instance, I want to control unique values for email and nickname. I created a list called ‘uniqueness’ with the unique properties. I overwritten method put in transactional mode and I wrote the hook _post_delete_hook when one entity is deleted.
4) Exception ENotUniqueException: custom exception class raised when some value is duplicated.
5) Procedure check_uniqueness: check whether a value is duplicated.
6) Procedure delete_uniqueness: delete unique values when the main entity is deleted.
Any tips or improvement are welcome.
class UniqueCategory(ndb.Model):
# Key = [kind name].[property name]
class Unique(ndb.Model):
# Parent = UniqueCategory
# Key = property value
reference_urlsafe = ndb.StringProperty(required=True)
class ENotUniqueException(Exception):
def __init__(self, property_name):
super(ENotUniqueException, self).__init__('Property value {0} is duplicated'.format(property_name))
self. property_name = property_name
class User(ndb.Model):
# Key = Firebase UUID or automatically generated
firstName = ndb.StringProperty(required=True)
surname = ndb.StringProperty(required=True)
nickname = ndb.StringProperty(required=True)
email = ndb.StringProperty(required=True)
#ndb.transactional(xg=True)
def put(self):
result = super(User, self).put()
check_uniqueness (self)
return result
#classmethod
def _post_delete_hook(cls, key, future):
delete_uniqueness(key)
uniqueness = [nickname, email]
def check_uniqueness(entity):
def get_or_insert_unique_category(qualified_name):
unique_category_key = ndb.Key(UniqueCategory, qualified_name)
unique_category = unique_category_key.get()
if not unique_category:
unique_category = UniqueCategory(id=qualified_name)
unique_category.put()
return unique_category_key
def del_old_value(key, attribute_name, unique_category_key):
old_entity = key.get()
if old_entity:
old_value = getattr(old_entity, attribute_name)
if old_value != new_value:
unique_key = ndb.Key(Unique, old_value, parent=unique_category_key)
unique_key.delete()
# Main flow
for unique_attribute in entity.uniqueness:
attribute_name = unique_attribute._name
qualified_name = type(entity).__name__ + '.' + attribute_name
new_value = getattr(entity, attribute_name)
unique_category_key = get_or_insert_unique_category(qualified_name)
del_old_value(entity.key, attribute_name, unique_category_key)
unique = ndb.Key(Unique, new_value, parent=unique_category_key).get()
if unique is not None and unique.reference_urlsafe != entity.key.urlsafe():
raise ENotUniqueException(attribute_name)
else:
unique = Unique(parent=unique_category_key,
id=new_value,
reference_urlsafe=entity.key.urlsafe())
unique.put()
def delete_uniqueness(key):
list_of_keys = Unique.query(Unique.reference_urlsafe == key.urlsafe()).fetch(keys_only=True)
if list_of_keys:
ndb.delete_multi(list_of_keys)
I use JPA->Hibernate. PlayFramework. I want to have relationship.
Category - 1:n -> Tag
Every category can have many tags, but tags do not know about it.
So, i do like this:
#Entity
public class Category ... {
#OneToMany
public List<Tag> tags = new LinkedList<Tag>();
}
I have test:
#Test
public void playWithTags() {
Tag tag1 = new Tag("tag1").save(); // managed by playframework
Category cat1 = new Category("cat1");
cat1.tags.add(tag1);
cat1.save();
// check if tag1 and cat1 were saved
assertEquals(1, Tag.count());
assertEquals(1, Category.count());
Category cat2 = new Category("cat2");
cat2.tags.add(tag1);
cat2.save();
}
The result is:
16:18:01,555 ERROR ~ Duplicate entry '1' for key 'tags_id'
16:18:01,555 ERROR ~ Could not synchronize database state with session
org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:96)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelp
....
java:908)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.sql.BatchUpdateException: Duplicate entry '1' for key 'tags_id'
at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:2020)
It seems that cat2.save() try to do more then it should
If if use merge() instead of save() it works good:
cat2.merge();
BUT WHY?
I have fixed the problem. The problem was in that, that I used NOT THAT annotation. So i just changed #OneToMany to #ManyToMany and voilà - No any restrictions anymore.
But if saying about the OneToMany then it seems there was a unique-restriction on database-level which prevented us to put not-unique values to tags_id. Therefore we could not put same tag to One category. I.e. it wanted One category for Many tags, but if tags were already 'used' - no way.. I tried to put unique=true/false in #JoinTable -> #JoinColumn - but it does not help. For me it's still strange, but at least current problem was fixed.
You're mixing up two concepts: Primary key and foreign key.
There can be only one PK but FK just means "there must be an element with this ID in some other table". FK doesn't constrain uniqueness.
[EDIT] Your problem is that you're mixing entities. How did you get the tag1 which is returned by save()?
This entity must be one which you get from Hibernate, not the result from new. Even if it looks insane, you must do this in save():
session.save(tag);
return session.load(tag.getId());
This way, you get an entity that is managed by Hibernate. Only when the entity is managed by Hibernate, Hibernate knows when it has to save the entity and when it has already been saved.
So when you do cat2.tags.add(tag1); in your example above, Hibernate thinks "oh, I don't know anything about this tag, it must be a new one".
And tries to save the tag again.
I'm developping a web application using google appengine and django, but I think my problem is more general.
The users have the possibility to create tables, look: tables are not represented as TABLES in the database. I give you an example:
First form:
Name of the the table: __________
First column name: __________
Second column name: _________
...
The number of columns is not fixed, but there is a maximum (100 for example). The type in every columns is the same.
Second form (after choosing a particular table the user can fill the table):
column_name1: _____________
column_name2: _____________
....
I'm using this solution, but it's wrong:
class Table(db.Model):
name = db.StringProperty(required = True)
class Column(db.Model):
name = db.StringProperty(required = True)
number = db.IntegerProperty()
table = db.ReferenceProperty(table, collection_name="columns")
class Value(db.Model):
time = db.TimeProperty()
column = db.ReferenceProperty(Column, collection_name="values")
when I want to list a table I take its columns and from every columns I take their values:
data = []
for column in data.columns:
column_data = []
for value in column.values:
column_data.append(value.time)
data.append(column_data)
data = zip(*data)
I think that the problem is the order of the values, because it is not true that the order for one column is the same for the others. I'm waiting for this bug (but until now I never seen it):
Table as I want: as I will got:
a z c a e c
d e f d h f
g h i g z i
Better solutions? Maybe using ListProperty?
Here's a data model that might do the trick for you:
class Table(db.Model):
name = db.StringProperty(required=True)
owner = db.UserProperty()
column_names = db.StringListProperty()
class Row(db.Model):
values = db.ListProperty(yourtype)
table = db.ReferenceProperty(Table, collection_name='rows')
My reasoning:
You don't really need a separate entity to store column names. Since all columns are of the same data type, you only need to store the name, and the fact that they are stored in a list gives you an implicit order number.
By storing the values in a list in the Row entity, you can use an index into the column_names property to find the matching value in the values property.
By storing all of the values for a row together in a single entity, there is no possibility of values appearing out of their correct order.
Caveat emptor:
This model will not work well if the table can have columns added to it after it has been populated with data. To make that possible, every time that a column is added, every existing row belonging to that table would have to have a value appended to its values list. If it were possible to efficiently store dictionaries in the datastore, this would not be a problem, but list can really only be appended to.
Alternatively, you could use Expando...
Another possibility is that you could define the Row model as an Expando, which allows you to dynamically create properties on an entity. You could set column values only for the columns that have values in them, and that you could also add columns to the table after it has data in it and not break anything:
class Row(db.Expando):
table = db.ReferenceProperty(Table, collection_name='rows')
#staticmethod
def __name_for_column_index(index):
return "column_%d" % index
def __getitem__(self, key):
# Allows one to get at the columns of Row entities with
# subscript syntax:
# first_row = Row.get()
# col1 = first_row[1]
# col12 = first_row[12]
value = None
try:
value = self.__dict__[Row.__name_for_column_index]
catch KeyError:
# The given column is not defined for this Row
pass
return value
def __setitem__(self, key, value):
# Allows one to set the columns of Row entities with
# subscript syntax:
# first_row = Row.get()
# first_row[5] = "New values for column 5"
self.__dict__[Row.__name_for_column_index] = value
# In order to allow efficient multiple column changes,
# the put() can go somewhere else.
self.put()
Why don't you add an IntegerProperty to Value for rowNumber and increment it every time you add a new row of values and then you can reconstruct the table by sorting by rowNumber.
You're going to make life very hard for yourself unless your user's 'tables' are actually stored as real tables in a relational database. Find some way of actually creating tables and use the power of an RDBMS, or you're reinventing a very complex and sophisticated wheel.
This is the conceptual idea I would use:
I would create two classes for the data-store:
table this would serve as a
dictionary, storing the structure of
the pseudo-tables your app would
create. it would have two fields :
table_name, column_name,
column_order . where column_order
would give the position of the
column within the table
data
this would store the actual data in
the pseudo-tables. it would have
four fields : row_id, table_name,
column_name , column_data. row_id
would be the same for data
pertaining to the same row and would
be unique for data across the
various pseudo-tables.
Put the data in a LongBlob.
The power of a database is to be able to search and organise data so that you are able to get only the part you want for performances and simplicity issues : you don't want the whole database, you just want a part of it and want it fast. But from what I understand, when you retrieve a user's data, you retrieve it all and display it. So you don't need to sotre the data in a normal "database" way.
What I would suggest is to simply format and store the whole data from a single user in a single column with a suitable type (LongBlob for example). The format would be an object with a list of columns and rows of type. And you define the object in whatever language you use to communicate with the database.
The columns in your (real) database would be : User int, TableNo int, Table Longblob.
If user8 has 3 tables, you will have the following rows :
8, 1, objectcontaintingtable1;
8, 2, objectcontaintingtable2;
8, 3, objectcontaintingtable3;