iex(18)> fields = [:id]
[:id]
iex(19)> fields_map = %{id: :job_id}
%{id: :job_id}
iex(20)> query = from p in Qber.V1.JobModel, where: p.id == 1, select: map(p, ^fields)
#Ecto.Query<from j in Qber.V1.JobModel, where: j.id == 1, select: map(j, [:id])>
I want to select my fields dynamically with AS names on the basis of params I got(which may have some joins as this app is going to have heavy admin dashboard queries). So I need dynamic solution. is there a way I can pass a map instead of list dynamically to map function and ecto will send me the selected result with custom names I passed in map. Instead of
[%{id: 1}]
I want the result to be
[%{job_id: 1}]
Note: I have tried and searched different keywords on the web and I have gone through almost all the docs many times and unable to find solution.
Related
I have 2 tables contractPoint and contractPointHistory
ContractPointHistory
ContractPoint
I would like to get contractPoint where point will be subtracted by pointChange. For example: ContractPoint -> id: 3, point: 5
ContractPointHistory has contractPointId: 3 and pointChange: -5. So after manipulating point in contractPoint should be 0
I wrote this code, but it works just for getRawMany(), not for getMany()
const contractPoints = await getRepository(ContractPoint).createQueryBuilder('contractPoint')
.addSelect('"contractPoint".point + COALESCE((SELECT SUM(cpHistory.point_change) FROM contract_point_history AS cpHistory WHERE cpHistory.contract_point_id = contractPoint.id), 0) AS points')
.andWhere('EXTRACT(YEAR FROM contractPoint.validFrom) = :year', { year })
.andWhere('contractPoint.contractId = :contractId', { contractId })
.orderBy('contractPoint.grantedAt', OrderByDirection.Desc)
.getMany();
The method getMany can be used to select all attributes of an entity. However, if one wants to select some specific attributes of an entity then one needs to use getRawMany.
As per the documentation -
There are two types of results you can get using select query builder:
entities or raw results. Most of the time, you need to select real
entities from your database, for example, users. For this purpose, you
use getOne and getMany. But sometimes you need to select some specific
data, let's say the sum of all user photos. This data is not an
entity, it's called raw data. To get raw data, you use getRawOne and
getRawMany
From this, we can conclude that the query which you want to generate can not be made using getMany method.
I want to find a match between a database result set of a user and result sets of friends.
First I'm making a call to the database to get the ids of the user items:
$user_simp_items = Item::select('simp_id')->where('user_id', $user_id)->get();
Then I loop through the friends and make a call to get their item ids:
$friend_simp_items = Item::select('simp_id')->where('user_id', $friend_id)->get();
To find the matching ids I want to perform an INNER JOIN on the result sets. How do I do this in Laravel?
I'd like to do something like inner_join($user_simp_items, $friend_simp_items) and get the result set with only the matching items.
I used the toArray Eloquent method and then did an array_filter to get the intersecting elements.
Considering I have the following relationships:
class House(Model):
name = ...
class User(Model):
"""The standard auth model"""
pass
class Alert(Model):
user = ForeignKey(User)
house = ForeignKey(House)
somevalue = IntegerField()
Meta:
unique_together = (('user', 'property'),)
In one query, I would like to get the list of houses, and whether the current user has any alert for any of them.
In SQL I would do it like this:
SELECT *
FROM house h
LEFT JOIN alert a
ON h.id = a.house_id
WHERE a.user_id = ?
OR a.user_id IS NULL
And I've found that I could use prefetch_related to achieve something like this:
p = Prefetch('alert_set', queryset=Alert.objects.filter(user=self.request.user), to_attr='user_alert')
houses = House.objects.order_by('name').prefetch_related(p)
The above example works, but houses.user_alert is a list, not an Alert object. I only have one alert per user per house, so what is the best way for me to get this information?
select_related didn't seem to work. Oh, and surely I know I can manage this in multiple queries, but I'd really want to have it done in one, and the 'Django way'.
Thanks in advance!
The solution is clearer if you start with the multiple query approach, and then try to optimise it. To get the user_alerts for every house, you could do the following:
houses = House.objects.order_by('name')
for house in houses:
user_alerts = house.alert_set.filter(user=self.request.user)
The user_alerts queryset will cause an extra query for every house in the queryset. You can avoid this with prefetch_related.
alerts_queryset = Alert.objects.filter(user=self.request.user)
houses = House.objects.order_by('name').prefetch_related(
Prefetch('alert_set', queryset=alerts_queryset, to_attrs='user_alerts'),
)
for house in houses:
user_alerts = house.user_alerts
This will take two queries, one for houses and one for the alerts. I don't think you require select related here to fetch the user, since you already have access to the user with self.request.user. If you want you could add select_related to the alerts_queryset:
alerts_queryset = Alert.objects.filter(user=self.request.user).select_related('user')
In your case, user_alerts will be an empty list or a list with one item, because of your unique_together constraint. If you can't handle the list, you could loop through the queryset once, and set house.user_alert:
for house in houses:
house.user_alert = house.user_alerts[0] if house.user_alerts else None
By example:
r = Model.arel_table
s = SomeOtherModel.arel_table
Model.select(r[:id], s[:othercolumn].as('othercolumn')).
joins(:someothermodel)
Will product the sql:
`SELECT `model`.`id`, `someothermodel`.`othercolumn` AS othercolumn FROM `model` INNER JOIN `someothermodel` ON `model`.`id` = `someothermodel`.`model_id`
Which is correct. However, when the models are loaded, the attribute othercolumn is ignored because it is not an attribute of Model.
It's similar to eager loading and includes, but I don't want all columns, only the one specified so include is no good.
There must be an easy way of getting columns from other models? I'd preferably have the items return as instances of Model than simple arrays/hashes
When you do a select with joins or includes, you will be returned an ActiveRecordRelation. This ActiveRecordRelation is composed of only the objects of the class which you use to call select on. The selected columns from the joined models are added to the objects returned. Because these attributes are not Model's attribute they don't show up when you inspect these objects, and I believe this is the primary reason for confusion.
You could try this out in your rails console:
> result = Model.select(r[:id], s[:othercolumn].as('othercolumn')).joins(:someothermodel)
=> #<ActiveRecord::Relation [#<Model id: 1>]>
# "othercolumn" is not shown in the result but doing the following will yield correct result
> result.first.othercolumn
=> "myothercolumnvalue"
I have a database table called Event which in CakePHP has its relationships coded to like so:
var $belongsTo = array('Sport');
var $hasOne = array('Result', 'Point', 'Writeup', 'Timetable', 'Photo');
Now am doing a query and only want to pull out Sport, Point, and Timetable
Which would result in me retrieving Sports, Events, Points, and Timetable.
Reason for not pulling everything is due the results having 17000+ rows.
Is there a way to only select those tables using:
$this->Event->find('all');
I have had a look at the API but can't see how its done.
You should set recursive to -1 in your app_model and only pull the things you require. never use recursive of 2 and http://book.cakephp.org/view/1323/Containable is awesome.
just $this->Event->find('all', array('contain' => array()));
if you do the trick of recursive as -1 in app_model, this is not needed, if would just be find('all') like you have