I have a very complex sql query that I would like to convert to RoR's ORM.
SELECT c.* FROM (SELECT companies.* FROM companies WHERE city = "?" AND country = "?") AS c INNER JOIN tagsForCompany AS tc ON c.id = tc.Company INNER JOIN tags AS t ON t.id = tc.TID WHERE t.Name REGEXP '?'
I have defined the models like this:
companies.rb
class Company < ActiveRecord::Base
# ... Some code that doesn't matter
has_and_belongs_to_many :tags
# ... Some other code
end
and tags.rb
class Tag < ActiveRecord::Base
has_and_belongs_to_many :company
end
I need a function in the companies controller that searches for the companies like the query above.
Options:
First: find_by_sql()
Description: Allows you to put any query you want on it.
http://apidock.com/rails/ActiveRecord/Base/find_by_sql/class
Second: Combination of .where() and .joins() method.
But be careful, if you call .joins() after a .where() with a nil return, you will get an error of undefined method. The solution here would be to first test if .where() returned anything, then you can join with another table.
Possible ways to use joins:
joins(:tags) Creates a Inner Join
joins('Left join foo...') Enables you to use left outter joins
joins(tagsForCompanies: :tags) Nested Joins if you have N to N associations.
See API:
http://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html#method-i-where
http://guides.rubyonrails.org/active_record_querying.html#joining-tables
Related
I am looking to run the following query in Rails (I have used the scuttle.io site to convert my SQL to rails-friendly syntax):
Here is the original query:
SELECT pools.name AS "Pool Name", COUNT(DISTINCT stakings.user_id) AS "Total Number of Users Per Pool" from stakings
INNER JOIN pools ON stakings.pool_id = pools.id
INNER JOIN users ON users.id = stakings.user_id
INNER JOIN countries ON countries.code = users.country
WHERE countries.kyc_flow = 1
GROUP BY (pools.name);
And here is the scuttle.io query:
<%Staking.select(
[
Pool.arel_table[:name].as('Pool_Name'), Staking.arel_table[:user_id].count.as('Total_Number_of_Users_Per_Pool')
]
).where(Country.arel_table[:kyc_flow].eq(1)).joins(
Staking.arel_table.join(Pool.arel_table).on(
Staking.arel_table[:pool_id].eq(Pool.arel_table[:id])
).join_sources
).joins(
Staking.arel_table.join(User.arel_table).on(
User.arel_table[:id].eq(Staking.arel_table[:user_id])
).join_sources
).joins(
Staking.arel_table.join(Country.arel_table).on(
Country.arel_table[:code].eq(User.arel_table[:country])
).join_sources
).group(Pool.arel_table[:name]).each do |x|%>
<p><%=x.Pool_Name%><p>
<p><%=x.Total_Number_of_Users_Per_Pool%>
<%end%>
Now, as you may notice, sctuttle.io does not include the distinct parameter which I need. How in the world can I use distinct here without getting errors such as "method distinct does not exist for Arel Node?" or just syntax errors?
Is there any way to write the above query using rails ActiveRecord? I am sure there is, but I am really not sure how.
Answer
The Arel::Nodes::Count class (an Arel::Nodes::Function) accepts a boolean value for distinctness.
def initialize expr, distinct = false, aliaz = nil
super(expr, aliaz)
#distinct = distinct
end
The #count expression is a shortcut for the same and also accepts a single argument
def count distinct = false
Nodes::Count.new [self], distinct
end
So in your case you could use either of the below options
Arel::Nodes::Count.new([Staking.arel_table[:user_id]],true,'Total_Number_of_Users_Per_Pool')
# OR
Staking.arel_table[:user_id].count(true).as('Total_Number_of_Users_Per_Pool')
Suggestion 1:
The Arel you have seems a bit overkill. Given the natural relationships you should be able to simplify this a bit e.g.
country_table = Country.arel_table
Staking
.joins(:pools,:users)
.joins( Arel::Nodes::InnerJoin(
country_table,
country_table.create_on(country_table[:code].eq(User.arel_table[:country])))
.select(
Pool.arel_table[:name],
Staking.arel_table[:user_id].count(true).as('Total_Number_of_Users_Per_Pool')
)
.where(countries: {kyc_flow: 1})
.group(Pool.arel_table[:name])
Suggestion 2: Move this query to your controller. The view has no business making database calls.
Entities :
Model
Category
Keyword
Model has a many to many relationship to keyword as well as category has a many to many relationship to keyword.
The orm generates following tables
model
category
keyword
keyword_model
keyword_category
When a category is given, how can I get all models related to this category? I would do it like this
get all keyword id's from keyword_category by category.id
join the result with the keyword_model table
the result of the join should be all relevant model id's
Since symfony2 deals with entities and not tables it seems hard to create a mysql query. I tried with something like
SELECT x,y FROM MyBundle:Category x, MyBundle:Model y
JOIN x.keywords
JOIN y.keywords
WHERE
x.id = " . $category . "
however this is invalid mysql syntax. Any ideas how to get the models here?
You could try the following:
SELECT
y
FROM
MyBundle:Model y
WHERE
EXISTS (
SELECT
x
FROM
MyBundle:Category x
JOIN
x.keywords xk
WHERE
xk MEMBER OF y.keywords AND
x = :category
)
Or if your relations are bidirectional:
SELECT
y
FROM
MyBundle:Model y
JOIN
y.keywords yk
JOIN
yk.categories c
WHERE
c = :category
From a given category (I suppose that you have the id)
$category_repo = $this->getDoctrine()->getManager()->getRepository('YourBundleName:Category');
$category = $category_repo->findOneById($id); //$id is your entity id
$keywords = $category->getKeywords(); //getKeywords() is the name of the method that you should have inside your class
$models = new ArrayCollection(); //or use a simple array
foreach($keywords as $keyword) {
foreach($keyword->getModels() as $model) {
$models->add($model);
}
}
however use sql directly should be more performing as you'll do a single query instead of a query (lazy-loading concept) for each object
I have a Student model and a Gpa model. Student has_many Gpa. How would I sort students based on their most recently created gpa record's value attribute?
NOTE: I don't want to sort an individual student's GPAs based on the created date. I would like to pull ALL students and sort them based on their most recent GPA record
class Student < ActiveRecord::Base
has_many :gpas
end
#students = Student.order(...)
assuming the gpas timestamp is updated_at
Student.joins(:gpas).order('gpas.updated_at DESC').uniq
To include students without gpas
#references is rails 4; works in rails 3 without it
Student.includes(:gpas).order('gpas.updated_at DESC').references(:gpas).uniq
if you dont like the distinct that uniq creates, you can use some raw sql
Student.find_by_sql("SELECT students.* FROM students
INNER JOIN gpas ON gpas.student_id = students.id
LEFT OUTER JOIN gpas AS future ON future.student_id = gpas.student_id
AND future.updated_at > gpas.updated_at
WHERE future.id IS NULL ORDER BY gpas.updated_at DESC")
# or some pretty raw arel
gpa_table = Gpa.arel_table
on = Arel::Nodes::On.new(
Arel::Nodes::Equality.new(gpa_table[:student_id], Student.arel_table[:id])
)
inner_join = Arel::Nodes::InnerJoin.new(gpa_table, on)
future_gpa_table = Gpa.arel_table.alias("future")
on = Arel::Nodes::On.new(
Arel::Nodes::Equality.new(future_gpa_table[:student_id], gpa_table[:student_id]).\
and(future_gpa_table[:updated_at].gt(gpa_table[:updated_at])
)
)
outer_join = Arel::Nodes::OuterJoin.new(future_gpa_table, on)
# get results
Student.joins(inner_join).joins(outer_join).where("future.id IS NULL").\
order('gpas.updated_at DESC')
I'm not sure that there's a way of achieving this in any kind of convenient and mostly-ruby way. The SQL required for an efficient implementation probably requires an order based on join -- something like ...
select
...
from
students
order by
( select gpas.value
from gpas
where gpas.student_id = student.id
order by gpas.as_of_date desc
limit 1)
I'm not sure if that's legal in MySQL, but if it is you could probably just:
Student.order("(select gpas.value from gpas where gpas.student_id = student.id order by gpas.as_of_date desc limit 1)")
On the other hand, it seems like the last value would be an important one, so you might like to implement a callback on gpas to set a "last_gpa_id" or "last_gpa_value" in the students table to make this common join more efficient.
Then of course the implementation would be trivial.
#students = Student.includes(:gpas).order('gpas.value DESC')
Still it's important to note that this will include Students, who has got no gpas. But you can filter that easly out with #students.delete_if{ |s| s.gpas.blank? }
Probably something like
Student.joins(:gpas).order("gpas.value DESC")
You could try adding some options to the relationships in your models.
Something like:
class Student < ActiveRecord::Base
has_many :gpas, order: "value DESC", conditions: "foo = bar" #<-whatever conditions you want here
end
class Gpa < ActiveRecord::Base
belongs_to :student
end
Using options, all you have to do make a call and let Rails do most of the heavy lifting.
If you get stumped, there are several more options here: http://guides.rubyonrails.org/association_basics.html
Just do a keyword search on the page for "The has_and_belongs_to_many association supports these options:"
This should work for you.
Try this SQL query
SELECT * FROM students WHERE id IN
(SELECT student_id
FROM gpa
GROUP BY student_id
ORDER BY created_at DESC);
I think, you could try this method:
class Student < ActiveRecord::Base
attr_accessible :name
has_many :gpas
def self.by_last_gpas
sql = <<-SQL
select students.*,
(
select gpas.created_at from gpas where student_id=students.id
order by gpas.created_at desc
limit 1
) as last_created_at
from students
order by last_created_at desc
SQL
Student.find_by_sql(sql)
end
end
Quick and dirty:
You can somehow implement a query like this to fetch AR objects you need:
select s.* from students s, gpas g
where s.id = gpas.student_id
and gpas.id in (select max(id) from gpas group by student_id)
order by gpas.value
Assuming that id is higher for records with higher created_at.
OR
Nicer way:
I assume, you'll need student's last GPA score very often. Why not add a new column :last_gpa_score to Student model?
You can use callback to keep this field consistent and autofilled, i. e.:
class Gpa < ActiveRecord::Base
belongs_to :student
after_save :update_student_last_score
private
def update_student_last_score
self.student.update_last_gpa_score
end
end
class Student < ActiveRecord::Base
has_many :gpas
def update_last_gpa_score
self.last_gpa_score = self.gpas.order("created_at DESC").first.value
end
end
Then you can do whatever you like with last_gpa_score field on student.
You'll have to adjust the table names and column names to match your DB.
SELECT s.*, g.*
FROM (SELECT studentId, MAX(gpaDate) as gpaDate FROM gpas GROUP BY studentId) maxgpa
JOIN gpas g
ON g.studentid = maxgpa.studentId
AND g.gpaDate = maxgpa.gpaDate
JOIN students s
ON s.studentId = g.studentId
ORDER g.gpaDate DESC
Create a last_gpa method to get the last GPA created and then perform a standard Ruby sort.
def last_gpa
a.gpas.order(:order=>"created_at DESC").first
end
Student.all.sort { |a, b| a.last_gpa <=> b.last_gpa }
I'd really like to do the following query with the help with active record
(select *
from people p join cities c join services s
where p.city_id = c.id and p.id = s.person_id and s.type = 1)
intersect
(select *
from people p join cities c join services s
where p.city_id = c.id and p.id = s.person_id and s.type = 2)
Problem is, first of all, mysql doesn't support intersect. However, that can be worked around of. The thing is that I can get active record to output anything even close to that.
In active record the best I could do was to issue multiple queries then use reduce :& to join them, but then I get an Array, not a Relation. That's a problem for me because I want to call things like limit, etc. Plus, I think it would be better to the intersection to be done by the database, rather than ruby code.
Your question is probably solvable without intersection, something like:
Person.joins(:services).where(services: {service_type: [1,2]}).group(
people: :id).having('COUNT("people"."id")=2')
However the following is a general approach I use for constructing intersection like queries in ActiveRecord:
class Service < ActiveRecord::Base
belongs_to :person
def self.with_types(*types)
where(service_type: types)
end
end
class City < ActiveRecord::Base
has_and_belongs_to_many :services
has_many :people, inverse_of: :city
end
class Person < ActiveRecord::Base
belongs_to :city, inverse_of: :people
def self.with_cities(cities)
where(city_id: cities)
end
def self.with_all_service_types(*types)
types.map { |t|
joins(:services).merge(Service.with_types t).select(:id)
}.reduce(scoped) { |scope, subquery|
scope.where(id: subquery)
}
end
end
Person.with_all_service_types(1, 2)
Person.with_all_service_types(1, 2).with_cities(City.where(name: 'Gold Coast'))
It will generate SQL of the form:
SELECT "people".*
FROM "people"
WHERE "people"."id" in (SELECT "people"."id" FROM ...)
AND "people"."id" in (SELECT ...)
AND ...
You can create as many subqueries as required with the above approach based on any conditions/joins etc so long as each subquery returns the id of a matching person in its result set.
Each subquery result set will be AND'ed together thus restricting the matching set to the intersection of all of the subqueries.
UPDATE
For those using AR4 where scoped was removed, my other answer provides a semantically equivalent scoped polyfil which all is not an equivalent replacement for despite what the AR documentation suggests. Answer here: With Rails 4, Model.scoped is deprecated but Model.all can't replace it
I was struggling with the same issue, and found only one solution: multiple joins against the same association. This may not be too rails-ish since I'm constructing the SQL string for the joins, but I haven't found another way. This will work for an arbitrary number of service types (cities doesn't seem to factor in, so that join was omitted for clarity):
s = [1,2]
j = ''
s.each_index {|i|
j += " INNER JOIN services s#{i} ON s.person_id = people.id AND s#{i}.type_id = #{s[i]}"
}
People.all.joins(j)
I have a question about symfony2.
I have a project and I am using databases with it. I use for the most part Doctrine2 and entity classes. I like the entity class object database stuff, very handy etc.
My question is, is there a way to perform normal SQL in symfony? I always get an exception when I try to use standard SQL. I am having trouble with joins in doctrine2, so i would rather use normal SQL for that.
My join would look like this in SQL:
SELECT DISTINCT Document . *
FROM Document
INNER JOIN DocumentGruppe ON Document.id = DocumentGruppe.dokId
INNER JOIN UserGruppe ON DocumentGruppe.gruppenId = UserGruppe.gruppenId
WHERE UserGruppe.userId =9
The where clause at the end is just for testing. If I use doctrine with it's DQL it always says that there is an exception: The Variable DocumentGruppe was not defined before.
Here is my DQL query:
$test = $em->createQuery(
'SELECT DISTINCT d
FROM AcmeDocumentBundle:Document d
INNER JOIN DocumentGruppe dg ON d.id = dg.dokId
INNER JOIN UserGruppe ug ON dg.gruppenId = ug.gruppenId
WHERE ug.userId =9
'
);
Does anyone know a workaround or a way to use this doctrine2 stuff to work with joins?
Every JOINED tables must be declared as associations in mapping... How is your entity defined ? Show us your mapping file (Document.php if annotation, or Resources/config/doctrine/document;xml or yml if XMl or YAML).
Your request will be something like that :
$test = $em->createQuery(
'SELECT DISTINCT d
FROM AcmeDocumentBundle:Document d
INNER JOIN d.documentGruppen dg
INNER JOIN d.userGruppen ug
WHERE ug.userId =9
'
);