I am using SQLAlchemy 1.4.3.
Starting from this very basic example :
class User(Base):
id= Column(INTEGER(10), primary_key=True)
symbols = relationship('Symbol', lazy="noload")
Then during a query, I change the relationship Loading technique from lazy='noload' to lazy='joined' with :
res = self.session.query(User).options(joinedload(User.symbols)).all()
From the result (res and only with that data) how can I get the current value of the relationship loading technique of the symbol relationship?
There are several ways to get this value at the Drug model level like :
res[0].__dict__.['_sa_instance_state'].mapper.relationships
(not the easiest one though). in this example, it will give me with the 'lazy' key : 'noload' which is the value at the model level.
But I am not able to get the updated value of the relationship loading technique matching the query done. (which should be lazy='joined')
Any help would be greatly appreciated.
Thanks
A detailled explanation of how SQLAlchemy works for this part can be found on this thread : https://github.com/sqlalchemy/sqlalchemy/issues/6156
Related
I make a query (with \yii\db\ActiveQuery) with joins, and some fields in "where" clause become ambigous. Is there a nice and short way to specify the name of the current model`s (ActiveRecord) table (from which one the ActiveQuery was instantiated) before the column name? So I can use this all the time in all cases and to make it short.
Don't like doing smth like this all the time (especially in places where there're no joins, but just to be able to use those methods with joins if it will be needed):
// in the ActiveQuery method initialized from the model with tableName "company"
$this->andWhere(['{{%company}}.`company_id`' => $id]);
To make the "named scopes" to work for some cases with joins..
Also, what does the [[..]] mean in this case, like:
$this->andWhere(['[[company_id]]' => $id]);
Doesn't seem to work like to solve the problem described above.
Thx in advance!
P.S. sorry, don't have enough reputation to create tag yii2-active-query
to get real table name :
Class :
ModelName::getTableSchema()->fullName
Object :
$model::getTableSchema()->fullName
Your problem is a very common one and happens most often with fields liek description, notes and the like.
Solution
Instead of
$this->andWhere(['description'=>$desc]);
you simply write
$this->andWhere(['mytable.description'=>$desc]);
Done! Simply add the table name in front of the field. Both the table name and the field name will be automatically quoted when the raw SQL is created.
Pitfall
The above example solves your problem within query classes. One I struggled over and took me quite some time to solve was a models relations! If you join in other tables during your queries (more than just one) you could also run into this problem because your relation-methods within the model are not qualified.
Example: If you have three tables: student, class, and teacher. Student and teacher probably are in relation with class and both have a FK-field class_id. Now if you go from student via class to teacher ($student->class->teacher). You also get the ambigous-error. The problem here is that you should also qualify your relation definitions within the models!
public function getTeacher()
{
return $this->hasOne(Teacher::className(), ['teacher.id' => 'class.teacher_id']);
}
Proposal
When developing your models and query-classes always fully qualify the fields. You will never ever run into this problem again...that was my experience at least! I actually created my own model-gii-template. So this gets solved automatically now ;)
Hope it helped!
I am struggling with a basic problem. i am using cake php 2.5. i try to apply the find query in the company model and receiving all the data from companies and with its associations, but i only want to receive the data from company table and want to exclude the data from rest of relationships, can anyone help me with this. below are my queries.
$this->loadModel('Company');
$fields=array('id','name','logo','status');
$conditions=array('status'=>1);
$search_companies = $this->Company->find('first',
compact(array('conditions'=>$conditions,'fields'=>$fields)));
print_r($search_companies);die();
echo json_encode($search_companies);die();
With out seeing your data output, I am just going to take a stab at the problem.
Inside your $search_companies variable you are getting a multidimensional array probably with the other values of the other tables.
Why not just select the one array:
$wantedData = $search_companies['Company'];
// The key Company (which is the model) should be the data you are wanting.
Try setting model's recursive value to -1
$this->Company->recursive = -1;
$search_companies = $this->Company->find('first',
compact(array('conditions'=>$conditions,'fields'=>$fields)));
With this you will not fire the joins queries and therefore you only retrieve model's information.
Cakephp provide this functionality that we can unblind few/all associations on a any model. the keyword unbindModel is used for this purpose. inside the unblindModel you can define the association type and model(s) name that you want to unblind for that specific association.
$this->CurrentModelName->unbindModel(array('AssociationName' => array('ModelName_Youwwant_unblind')));
For a simple return all results query should one method be preferred over the other? I can find uses of both online but can't really find anything describing the differences.
db.session.query([my model name]).all()
[my model name].query.all()
I feel that [my model name].query.all() is more descriptive.
It is hard to give a clear answer, as there is a high degree of preference subjectivity in answering this question.
From one perspective, the db.session is desired, because the second approach requires it to be incorporated in your model as an added step - it is not there by default as part of the Base class. For instance:
Base = declarative_base()
DBSession = scoped_session(sessionmaker())
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)
fullname = Column(String)
password = Column(String)
session = Session()
print(User.query)
That code fails with the following error:
AttributeError: type object 'User' has no attribute 'query'
You need to do something like this:
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)
fullname = Column(String)
password = Column(String)
query = DBSession.query_property()
However, it could also be argued that just because it is not enabled by default, that doesn't invalidate it as a reasonable way to launch queries. Furthermore, in the flask-sqlalchemy package (which simplifies sqlalchemy integration into the flask web framework) this is already done for you as part of the Model class (doc). Adding the query property to a model can also be seen in the sqlalchemy tutorial (doc):
class User(object):
query = db_session.query_property()
....
Thus, people could argue either approach.
I personally have a preference for the second method when I am selecting from a single table. For example:
serv = Service.query.join(Supplier, SupplierUsr).filter(SupplierUsr.username == usr).all()
This is because it is of smaller line length and still easily readable.
If am selecting from more than one table or specifying columns, then I would use the model query method as it extracting information from more than one model.
deliverables = db.session.query(Deliverable.column1, BatchInstance.column2).\
join(BatchInstance, Service, Supplier, SupplierUser). \
filter(SupplierUser.username == str(current_user)).\
order_by(Deliverable.created_time.desc()).all()
That said, a counter argument could be made in always using the session.query method as it makes the code more consistent, and when reading left to right, the reader immediately knows that the sqlalchemy directive they are going to read will be query, before mentally absorbing what tables and columns are involved.
At the end of the day, the answer to your question is subjective and there is no correct answer, and any code readability benefits either way are tiny. The only thing where I see a strong benefit is not to use model query if you are selecting from many tables and instead use the session.query method.
I am designing a Web Application using Django Framework. I have written the model code, urls.py and view code which can be seen Here.
I have added some data into the database table. But when I try to access the object using the code below, it just shows bookInfo objects five times. I don't think I am successful enough in pulling the data from the database. Kindly help.
View
def showbooks(request):
booklist = bookInfo.objects.order_by('Name')[:10]
output = ','.join([str(id) for id in booklist])
return HttpResponse(output)
You are iterating through the object list, you just need to reference the column/attribute you want:
output = ','.join([obj.id for obj in booklist])
Alternatively you can more more finely craft you original db call, then the iterable you use will work. In this case we'll pull out a list of the 'id' attribute.
booklist = bookInfo.objects.order_by('Name').values_list('id', flat=True)[:10]
output = ','.join([id for id in booklist])
I think you are successful in pulling the data. It is just that booklist contains objects, not numeric ids. You can add __unicode__ method to you class BookInfo that is supposed to return a string representation of the object (probably book name in this case). This method is going to be invoked when str() is applied. You can find more info about __unicode__ here.
I'm learning sqlalchemy and not sure if I grasp it fully yet(I'm more used to writing queries by hand but I like the idea of abstracting the queries and getting objects). I'm going through the tutorial and trying to apply it to my code and ran into this part when defining a model:
def __repr__(self):
return "<User('%s','%s', '%s')>" % (self.name, self.fullname, self.password)
Its useful because I can just search for a username and get only the info about the user that I want but is there a way to either have multiple of these type of views that I can call? or am I using it wrong and should be writing a specific query for getting different data for different views?
Some context to why I'm asking my site has different templates, and most pages will just need the usersname, first/last name but some pages will require things like twitter or Facebook urls(also fields in the model).
First of all, __repr__ is not a view, so if you have a simple model User with defined columns, and you query for a User, all the columns will get loaded from the database, and not only those used in __repr__.
Lets take model Book (from the example refered to later) as a basis:
class Book(Base):
book_id = Column(Integer, primary_key=True)
title = Column(String(200), nullable=False)
summary = Column(String(2000))
excerpt = Column(Text)
photo = Column(Binary)
The first option to skip loading some columns is to use Deferred Column Loading:
class Book(Base):
# ...
excerpt = deferred(Column(Text))
photo = deferred(Column(Binary))
In this case when you execute query session.query(Book).get(1), the photo and excerpt columns will not be loaded until accessed from the code, at which point another query against the database will be executed to load the missing data.
But if you know before you query for the Book that you need the column photo immediately, you can still override the deferred behavior with undefer option: query = session.query(Book).options(undefer('photo')).get(1).
Basically, the suggestion here is to defer all the columns (in your case: except username, password etc) and in each use case (view) override with undefer those you know you need for that particular view. Please also see the group parameter of deferred, so that you can group the attributes by use case (view).
Another way would be to query only some columns, but in this case you are getting the tuple instance instead of the model instance (in your case User), so it is potentially OK for form filling, but not so good for model validation: session.query(Book.id, Book.title).all()