I have relation of relation of relation query thus and i want to select only the most recently created record for table CancellationRequest c.
Anyone any idea if this is/should be possible and how?
Doctrine_Query::create()
->from('UserNotificationTo unt')
->leftJoin('unt.Notification un')
->leftJoin('un.QuoteOrder qo')
->leftJoin('qo.CancellationRequest c')
->where('un.sent_external = 0')
->andWhere('c.updated_at *IS THE MOST RECENTLY CREATED ONE*')
->execute();
You have to do ORDER BY c.updated_at
Then you can do:
$userNotifcation->getQuoteOrder()->getCancellationRequest()->first()
to get the most recent one
Related
I need to update my database by adding one table, and one column to the existing table.
The new column and the table should have one-to-many relation.
here is the alembic revision file:
def upgrade():
op.create_table('categories',
sa.Column('category_id', sa.Integer, primary_key=True),
sa.Column('category_name', sa.String(30)),
sa.Relationship('post', backref='cat', lazy='dynamic') )
op.add_column('post', sa.Column('category', sa.Integer, sa.ForeignKey('categories.category_id')) )
The problem is with this line:
sa.Relationship('post', backref='cat', lazy='dynamic') )
What is the correct code to define relation here?
Thank You
Relationships are defined only on the SQLAlchemy side, not on the SQL side. Simply create the tables or columns that you need, and the relationship will work correctly. Therefore, it should not be in the migration.
Is it possible to prevent multiple querys when i use django ORM ? Example:
product = Product.objects.get(name="Banana")
for provider in product.providers.all():
print provider.name
This code will make 2 SQL querys:
1 - SELECT ••• FROM stock_product WHERE stock_product.name = 'Banana'
2 - SELECT stock_provider.id, stock_provider.name FROM stock_provider INNER JOIN stock_product_reference ON (stock_provider.id = stock_product_reference.provider_id) WHERE stock_product_reference.product_id = 1
I confess, i use Doctrine (PHP) for some projects. With doctrine it's possible to specify joins when retrieve the object (relations are populated in object, so no need to query database again for get attribute relation value).
Is it possible to do the same with Django's ORM ?
PS: I hop my question is comprehensive, english is not my primary language.
In Django 1.4 or later, you can use prefetch_related. It's like select_related but allows M2M relations and such.
product = Product.objects.prefetch_related('providers').get(name="Banana")
You still get two queries, though. From the docs:
prefetch_related, on the other hand, does a separate lookup for each relationship, and does the ‘joining’ in Python.
As for packing this down into a single query, Django won't do it like Doctrine because it doesn't do that much post-processing of the result set (Django would have to remove all the redundant column data, since you'll get a row per provider and each of these rows will have a copy of all of product's fields).
So if you want to pack this down to one query, you're going to have to turn it around and run the query on the Provider table (I'm guessing at your schema):
providers = Provider.objects.filter(product__name="Banana").select_related('product')
This should pack it down to one query, but you won't get a single product ORM object out of it, instead needing to get the product fields via providers[k].product.
You can use prefetch_related, sometimes in combination with select_related, to get all related objects in a single query: https://docs.djangoproject.com/en/1.5/ref/models/querysets/#prefetch-related
In MySQL, we can have foreign key relationships between tables in different databases. I am finding it difficult to translate this relationship on the respective Django models.
I have read in the docs that cross-db relationships are not supported, but can we override some property/function so that we can make tables be identified as DB.table rather than table?
For example, there is table table1 in DB1 that gets referenced in some table2 in DB2. Django tries (unsuccessfully) to find table1 in DB2, and raises a DatabaseError
Variable Value
charset 'latin1'
exc <class '_mysql_exceptions.ProgrammingError'>
self <MySQLdb.cursors.Cursor object at 0x2a87ed0>
args (195,)
db <weakproxy at 0x2a95208 to Connection at 0xdad0>
value ProgrammingError(1146, "Table 'DB2.table1' doesn't exist")
query 'SELECT (1) AS `a` FROM `table1` WHERE `table1`.`ndx` = 195 LIMIT 1'
Almost everything works, except the save method. A push in the right direction would help a lot!
You required Manually Selecting a Database.
Looking on the error you gave, you should do something like this:
qs = table1.objects.using('DB1 ').filter(pk=id)
# just an example
In this example we are explicitly telling Django to locate table1 in DB1.
It seems we cannot do anything to get relationships working between two tables in different mysql DBs. This is by design. Ticket 17875 has some info. We need to write code that works around this.
Can I have a DQL join between unrelated entities using WITH DQL operator? OR is definign relationship absolutely mandatory?
I have a unidirectional relationship with Category and CategorySubsription. Where CategorySubscription has a many to one unidirectional relationship with Category. I want to grab a list of Categories c and left join CategorySubscription cs WITH cs.category_id = c.id AND cs.user_id = value.
Can I do this somehow?
Starting with Doctrine version 2.3 you can, as mentioned in a blog.
It's also mentioned in the docs if you know where to look. Scroll down to the last example under "15.2.4. DQL SELECT Examples":
Joins between entities without associations were not possible until version 2.4, where you can generate an arbitrary join with the following syntax:
<?php
$query = $em->createQuery('SELECT u FROM User u JOIN Blacklist b WITH u.email = b.email');
I know it says "not possible until version 2.4", but it definitely works starting with 2.3!
You can try using multiple from() methods and join conditions put in where() or andWhere methods()
I know conditional filters aren't yet available for queries (as per "26.1.4. Applying Filter Rules to any Query" in the Known Limitations section of the Doctrine2 manual) , so I wanted to ask the experts what their preferred solution to the following problem is:
My site has product objects that each have many reviews. The reviews have a status field. I don't want to unnecessarily pull in reviews that haven't been approved during the automatic association that Doctrine2 does so wonderfully.
My current solution/hack is to use single table inheritance (STI) with a discriminator for "status" and have an ApprovedProductReview extending the ProductReview class based on a status of "APPROVED"
I should add that I am currently simply calling
$em->find('Entities\Product', $pid);
to get my product, and Doctrine2 does all the associations automatically. Should I instead be instantiating a product by providing a DQL query?
What I'd really like is a way to override the magic that Doctrine2 provides based on the annotations, and simply be able to use DQL to lazily get the correct subset of reviews.
Suggestions?
You can use the WITH statement in DQL:
$dql = "SELECT p, r
FROM Entities\Product p
LEFT JOIN p.reviews r WITH r.status = :status
WHERE p.id = :id"
$q = $em->createQuery($dql);
$q->setParameter('id', $id);
$q->setParameter('status', $status);
$product = $q->getSingleResult();