I have a simple model
class User
has_many :logs
class Logs
related in the usual way through the foreign key logs.user_id. I'm trying to do the following using Arel and according to the Arel doc it should work.
u_t = Arel::Table::new :users
l_t = Arel::Table::new :logs
counts = l_t.
group(l_t[:user_id]).
project(
l_t[:user_id].as("user_id"),
l_t[:user_id].count.as("count_all")
)
l_t.joins(counts).on(l_t[:id].eq(counts[:user_id]))
When I do that I get the error
TypeError: Cannot visit Arel::SelectManager
However the author of Arel explicitly suggests that Arel can do this kind of thing.
Please do not write responses on how I can achieve the same query with raw sql, another type of Arel query etc. It is the pattern I am interested in not the specific results of this query.
You can use join_sources to retrieve the Arel::Nodes::Join from the instance of Arel::SelectManager, and pass that to joins
Using your example:
l_t.joins(counts.join_sources).on(l_t[:id].eq(counts[:user_id]))
This achieves a join of nested select subquery with Arel:
You can add the nested inner_query and an outer_query scope in your Model file and use ...
inner_query = Model.inner_query(params)
result = Model.outer_query(params).joins(Arel.sql("(#{inner_query.to_sql})"))
.group("...")
.order("...")
For variations on this, for example to use INNER JOIN on the subquery, do the following:
inner_query = Model.inner_query(params)
result = Model.outer_query(params).joins(Arel.sql("INNER JOIN (#{inner_query.to_sql}) tablealias ON a.id = b.id"))
.group("...")
.order("...")
Add in the specific joins, constraints and groupings to each of the queries' scopes to modify the sql statement further ie:
scope :inner_query , -> (company_id, name) {
select("...")
.joins("left join table1 on table1.id = table2.id")
.where("table1.company_id = ? and table1.name in (?)", company_id, name)
.group("...")
}
This allows you to put WHERE conditions on the nested query as well as the outer query
Related
When querying one table using the doctrine query builder a partial select can be written like this:
$queryBuilder = $this->createQueryBuilder('person');
$queryBuilder->addSelect('partial person.{id, name}');
How can one write a partial select be written for a left joined table? I tried something like this, but can't figure out the correct syntax:
$queryBuilder = $this->createQueryBuilder('person');
$queryBuilder->join('person.address');
$queryBuilder->addSelect('partial person.{id, name} person.address.city'); // ???
My goal would be to select only parts of the Person and the Address object when executing the query to be more memory efficient.
Your syntax is off for your join operation. You have to give an alias when using join. From there, you can just use the same syntax to query your partial Address object:
// In a method of PersonRepository
$qb = $this->createQueryBuilder('person')
->select(['partial person.{id, name}', 'partial address.{id, city}'])
->join('person.address', 'address');
Notice that I added id to the fields retrieved for Address. If you don't, Doctrine will give you the following error:
Error: The partial field selection of class Path\To\Entity\Address must contain the identifier
As a side note, you said you wanted to write this select for a left joined table. If you want to perform a LEFT JOIN, you need to use leftJoin instead of join (the signature of both methods is the same).
I'm on laravel 5.1 using postgres as the DB. I have a fiddle here in case it helps understand my issue: https://www.db-fiddle.com/f/5ELU6xinJrXiQJ6u6VH5/4
with properties as (
select
properties.*,
json_agg(property_fields.*) as property_fields
from
properties
left join fields as property_fields
on property_fields.parent = 'property' and property_fields.parent_id = properties.id
group by properties.id, properties.deal_id, properties.address
)
select
deals.*,
json_agg(properties.*) as deal_properties,
json_agg(deal_fields.*) as deal_fields
from deals
left join properties on deals.id = properties.deal_id
left join fields deal_fields on deal_fields.parent = 'deal' and deal_fields.parent_id = deals.id
group by deals.id, deals.name
order by deals.id
Writing most of this is fairly straight forward. The problem I'm having is with the with properties as (...) block. I've tried something like:
DB::statement('WITH properties AS ( ... )')
->table('deals')
->select(' deals.*, json_agg(properties.*) as deal_properties, ')
...
->get();
But I notice the execution stop after DB::statement()
Is there a method in the Query Builder that I'm missing? How can I prefix my query with the WITH properties AS (...) statement?
I think it should also be noted that I'm trying to implement a Repository Pattern and I can't just wrap a DB::statement() around the whole query.
I've created a package for common table expressions: https://github.com/staudenmeir/laravel-cte
$query = 'select properties.*, [...]';
DB::table('deals')
->withExpression('properties', $query)
->leftJoin([...])
->[...]
You can also provide a query builder instance:
$query = DB::table('properties')
->select('properties.*', [...])
->leftJoin([...])
->[...]
DB::table('deals')
->withExpression('properties', $query)
->leftJoin([...])
->[...]
if you want some data fetch from a table you can use this type of code
$user = DB::table('table name')->where('name', 'John')->where('height','!>',"7")->select('table fields which you want to fetch')->get();
Or try using the larevel Eloquent ORM which will make things easier with the database.
for more example or reference
https://laravel.com/docs/5.0/queries
I think you can actually do this with eager loading,
assuming that the relationships are set up correctly.
(More reading here: https://laravel.com/docs/5.4/eloquent-relationships#constraining-eager-loads)
So I think you'd be able to add something like
->with(['properties' => function ($query) {
$query->select('field')
->leftJoin('join statement')
->groupBy('field1', 'field2');
}])
I am trying to convert a "raw" PostGIS SQL query into a Rails ActiveRecord query. My goal is to convert two sequential ActiveRecord queries (each taking ~1ms) into a single ActiveRecord query taking (~1ms). Using the SQL below with ActiveRecord::Base.connection.execute I was able to validate the reduction in time.
Thus, my direct request is to help me to convert this query into an ActiveRecord query (and the best way to execute it).
SELECT COUNT(*)
FROM "users"
INNER JOIN (
SELECT "centroid"
FROM "zip_caches"
WHERE "zip_caches"."postalcode" = '<postalcode>'
) AS "sub" ON ST_Intersects("users"."vendor_coverage", "sub"."centroid")
WHERE "users"."active" = 1;
NOTE that the value <postalcode> is the only variable data in this query. Obviously, there are two models here User and ZipCache. User has no direct relation to ZipCache.
The current two step ActiveRecord query looks like this.
zip = ZipCache.select(:centroid).where(postalcode: '<postalcode>').limit(1).first
User.where{st_intersects(vendor_coverage, zip.centroid)}.count
Disclamer: I've never used PostGIS
First in your final request, it seems like you've missed the WHERE "users"."active" = 1; part.
Here is what I'd do:
First add a active scope on user (for reusability)
scope :active, -> { User.where(active: 1) }
Then for the actual query, You can have the sub query without executing it and use it in a joins on the User model, such as:
subquery = ZipCache.select(:centroid).where(postalcode: '<postalcode>')
User.active
.joins("INNER JOIN (#{subquery.to_sql}) sub ON ST_Intersects(users.vendor_coverage, sub.centroid)")
.count
This allow minimal raw SQL, while keeping only one query.
In any case, check the actual sql request in your console/log by setting the logger level to debug.
The amazing tool scuttle.io is perfect for converting these sorts of queries:
User.select(Arel.star.count).where(User.arel_table[:active].eq(1)).joins(
User.arel_table.join(ZipCach.arel_table).on(
Arel::Nodes::NamedFunction.new(
'ST_Intersects', [
User.arel_table[:vendor_coverage], Sub.arel_table[:centroid]
]
)
).join_sources
)
Ok, I feel really stupid for asking this, but it's driving me nuts and I can't figure it out. The docs say I should be able to use select AS in a Rails/ActiveRecord query. So:
d = Dvd.where(id: 1).select("title AS my_title")
Is a valid query and if I do a to_sql on it, it produces the expected SQL:
SELECT title AS my_title FROM `dvd` WHERE `dvd`.`id` = 1
However, d.my_title will give an error:
NoMethodError: undefined method `my_title' for #<ActiveRecord::Relation
I need to be able to use AS since the columns I want to retrieve from different joins have the same name so I can't access them the "regular" way and have to resort to using AS.
I also don't want to resort to using find_by_sql for future compatibility and a possible switch form Mysql to PostGresql.
Just to clarify, what I'm really trying to do is write this SQL in a Railsy way:
SELECT tracks.name AS track_name, artists.name AS artist_name, composers.name AS composer_name, duration
FROM `tracks_cds`
INNER JOIN `tracks` ON `tracks`.`id` = `tracks_cds`.`track_id`
INNER JOIN `artists` ON `artists`.`id` = `tracks_cds`.`artist_id`
INNER JOIN `composers` ON `composers`.`id` = `tracks_cds`.`composer_id`
WHERE cd_id = cd.id
The top example was just a simplification of the fact that SELECT AS will not give you an easy way to refer to custom fields which I find hard to believe.
ActiveRecord automatically creates getter and setter methods for attributes based on the column names in the database, so there will be none defined for my_title.
Regarding the same common names, why not just do this:
d = Dvd.where(id: 1).select("dvds.title")
You can write your sql query and then just pass into ActiveRecord's execute method
query = "SELECT title AS my_title FROM `dvd` WHERE `dvd`.`id` = 1"
result = ActiveRecord::Base.connection.execute(query)
With SQL I can easily do sub-queries like this
User.where(:id => Account.where(..).select(:user_id))
This produces:
SELECT * FROM users WHERE id IN (SELECT user_id FROM accounts WHERE ..)
How can I do this using rails' 3 activerecord/ arel/ meta_where?
I do need/ want real subqueries, no ruby workarounds (using several queries).
Rails now does this by default :)
Message.where(user_id: Profile.select("user_id").where(gender: 'm'))
will produce the following SQL
SELECT "messages".* FROM "messages" WHERE "messages"."user_id" IN (SELECT user_id FROM "profiles" WHERE "profiles"."gender" = 'm')
(the version number that "now" refers to is most likely 3.2)
In ARel, the where() methods can take arrays as arguments that will generate a "WHERE id IN..." query. So what you have written is along the right lines.
For example, the following ARel code:
User.where(:id => Order.where(:user_id => 5)).to_sql
... which is equivalent to:
User.where(:id => [5, 1, 2, 3]).to_sql
... would output the following SQL on a PostgreSQL database:
SELECT "users".* FROM "users" WHERE "users"."id" IN (5, 1, 2, 3)"
Update: in response to comments
Okay, so I misunderstood the question. I believe that you want the sub-query to explicitly list the column names that are to be selected in order to not hit the database with two queries (which is what ActiveRecord does in the simplest case).
You can use project for the select in your sub-select:
accounts = Account.arel_table
User.where(:id => accounts.project(:user_id).where(accounts[:user_id].not_eq(6)))
... which would produce the following SQL:
SELECT "users".* FROM "users" WHERE "users"."id" IN (SELECT user_id FROM "accounts" WHERE "accounts"."user_id" != 6)
I sincerely hope that I have given you what you wanted this time!
I was looking for the answer to this question myself, and I came up with an alternative approach. I just thought I'd share it - hope it helps someone! :)
# 1. Build you subquery with AREL.
subquery = Account.where(...).select(:id)
# 2. Use the AREL object in your query by converting it into a SQL string
query = User.where("users.account_id IN (#{subquery.to_sql})")
Bingo! Bango!
Works with Rails 3.1
Another alternative:
Message.where(user: User.joins(:profile).where(profile: { gender: 'm' })
This is an example of a nested subquery using rails ActiveRecord and using JOINs, where you can add clauses on each query as well as the result :
You can add the nested inner_query and an outer_query scopes in your Model file and use ...
inner_query = Account.inner_query(params)
result = User.outer_query(params).joins("(#{inner_query.to_sql}) alias ON users.id=accounts.id")
.group("alias.grouping_var, alias.grouping_var2 ...")
.order("...")
An example of the scope:
scope :inner_query , -> (ids) {
select("...")
.joins("left join users on users.id = accounts.id")
.where("users.account_id IN (?)", ids)
.group("...")
}