If i use expression Model.find(1) then rails executes it as prepared statement: SELECT "models".* FROM "models" WHERE "models"."id" = $1 LIMIT 1 [["id", 1]]
But when I use Model.where("id = ?", 1) it executes without prepared statement: SELECT "models".* FROM "models" WHERE (id = 1)
How to force rails to use prepared statement in this case too?
i'm not sure you can.
But
Model.where(:id => 1)
Should generate a prepared statement. Fragment string works differently, so you can generate exactly what you need, in custom cases.
Edit :
Try this, i'm not sure it works, i can' test for now, but it looks like what you need :
Client.where("created_at >= :start_date AND created_at <= :end_date",
{:start_date => params[:start_date], :end_date => params[:end_date]})
More here: http://guides.rubyonrails.org/active_record_querying.html#conditions
In the placeholder section. Moreover date range works in the array format :
:date => date_begenning..date_end
Edit 2 : indeed you can, but i seems where don't support building this by hand.
You might build your prepared queries by hand :
http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/DatabaseStatements.html#method-i-exec_query
exec_query(sql, name = 'SQL', binds = [])
There is also a bind method on your relation.
But both binds need that the value have a name method, they will crash if you give a fixnum, a hash, ect. I hadn't found any doc explaining how this works.
Bu for the where clause, as long it is of Class String, active ecord apply a .to_sql on it, so you don't get your prepared statement.
Related
I have a Company model that has_many Statement.
class Company < ActiveRecord::Base
has_many :statements
end
I want to get statements that have most latest date field grouped by fiscal_year_end field.
I implemented the function like this:
c = Company.first
c.statements.to_a.group_by{|s| s.fiscal_year_end }.map{|k,v| v.max_by(&:date) }
It works ok, but if possible I want to use ActiveRecord query(SQL), so that I don't need to load unnecessary instance to memory.
How can I write it by using SQL?
select t.username, t.date, t.value
from MyTable t
inner join (
select username, max(date) as MaxDate
from MyTable
group by username
) tm on t.username = tm.username and t.date = tm.MaxDate
For these kinds of things, I find it helpful to get the raw SQL working first, and then translate it into ActiveRecord afterwards. It sounds like a textbook case of GROUP BY:
SELECT fiscal_year_end, MAX(date) AS max_date
FROM statements
WHERE company_id = 1
GROUP BY fiscal_year_end
Now you can express that in ActiveRecord like so:
c = Company.first
c.statements.
group(:fiscal_year_end).
order(nil). # might not be necessary, depending on your association and Rails version
select("fiscal_year_end, MAX(date) AS max_date")
The reason for order(nil) is to prevent ActiveRecord from adding ORDER BY id to the query. Rails 4+ does this automatically. Since you aren't grouping by id, it will cause the error you're seeing. You could also order(:fiscal_year_end) if that is what you want.
That will give you a bunch of Statement objects. They will be read-only, and every attribute will be nil except for fiscal_year_end and the magically-present new field max_date. These instances don't represent specific statements, but statement "groups" from your query. So you can do something like this:
- #statements_by_fiscal_year_end.each do |s|
%tr
%td= s.fiscal_year_end
%td= s.max_date
Note there is no n+1 query problem here, because you fetched everything you need in one query.
If you decide that you need more than just the max date, e.g. you want the whole statement with the latest date, then you should look at your options for the greatest n per group problem. For raw SQL I like LATERAL JOIN, but the easiest approach to use with ActiveRecord is DISTINCT ON.
Oh one more tip: For debugging weird errors, I find it helpful to confirm what SQL ActiveRecord is trying to use. You can use to_sql to get that:
c = Company.first
puts c.statements.
group(:fiscal_year_end).
select("fiscal_year_end, MAX(date) AS max_date").
to_sql
In that example, I'm leaving off order(nil) so you can see that ActiveRecord is adding an ORDER BY clause you don't want.
for example you want to get all statements by start of the months you should use this
#companey = Company.first
#statements = #companey.statements.find(:all, :order => 'due_at, id', :limit => 50)
then group them as you want
#monthly_statements = #statements.group_by { |statement| t.due_at.beginning_of_month }
Building upon Bharat's answer you can do this type of query in Rails using find_by_sql in this way:
Statement.find_by_sql ["Select t.* from statements t INNER JOIN (
SELECT fiscal_year_end, max(date) as MaxDate GROUP BY fiscal_year_end
) tm on t.fiscal_year_end = tm.fiscal_year_end AND
t.created_at = tm.MaxDate WHERE t.company_id = ?", company.id]
Note the last where part to make sure the statements belong to a specific company instance, and that this is called from the class. I haven't tested this with the array form, but I believe you can turn this into a scope and use it like this:
# In Statement model
scope :latest_from_fiscal_year, lambda |enterprise_id| {
find_by_sql[..., enterprise_id] # Query above
}
# Wherever you need these statements for a particular company
company = Company.find(params[:id])
latest_statements = Statement.latest_from_fiscal_year(company.id)
Note that if you somehow need all the latest statements for all companies then this most likely leave you with a N+1 queries problem. But that is a beast for another day.
Note: If anyone else has a way to have this query work on the association without using the last where part (company.statements.latest_from_year and such) let me know and I'll edit this, in my case in rails 3 it just pulled em from the whole table without filtering.
I am working with the RailsCast on token input and am trying to cleanup a query method for Postgres. I found this post for making my query DB-agnostic.
My method:
def self.tokens(query)
t = Language.arel_table
languages = Language.where(t[:name].matches("%#{query}%"))
if languages.empty?
[{id: "<<<#{query}>>>", name: "New: \"#{query}\""}]
end
end
Returns
:001 > Language.tokens('Ru')
(0.8ms) SELECT COUNT(*) FROM "languages" WHERE ("languages"."name" ILIKE '%Ru%')
But if I use return instead of language =, I get the correct query:
def self.tokens(query)
t = .arel_table
return Language.where(t[:name].matches("%#{query}%"))
end
:001 > Language.tokens('Ru')
Language Load (0.9ms) SELECT "languages".* FROM "languages" WHERE ("languages"."name" ILIKE '%Ru%')
It's probably something obvious, but I cannot figure out why the first method is selecting count instead of all of the rows in the `languages' table db. I would really like to store the result of that query in a variable.
It's because the where is resolved as lazily as it possibly can be (not until it is absolutely needed). In your case it needs it when you:
Explicitly return
Check empty?
The reason it is doing the count, is to determine via the count whether it is empty.
I am new to rails. What I see that there are a lot of ways to find a record:
find_by_<columnname>(<columnvalue>)
find(:first, :conditions => { <columnname> => <columnvalue> }
where(<columnname> => <columnvalue>).first
And it looks like all of them end up generating exactly the same SQL. Also, I believe the same is true for finding multiple records:
find_all_by_<columnname>(<columnvalue>)
find(:all, :conditions => { <columnname> => <columnvalue> }
where(<columnname> => <columnvalue>)
Is there a rule of thumb or recommendation on which one to use?
where returns ActiveRecord::Relation
Now take a look at find_by implementation:
def find_by
where(*args).take
end
As you can see find_by is the same as where but it returns only one record. This method should be used for getting 1 record and where should be used for getting all records with some conditions.
Edit:
This answer is very old and other, better answers have come up since this post was made. I'd advise looking at the one posted below by #Hossam Khamis for more details.
Use whichever one you feel suits your needs best.
The find method is usually used to retrieve a row by ID:
Model.find(1)
It's worth noting that find will throw an exception if the item is not found by the attribute that you supply. Use where (as described below, which will return an empty array if the attribute is not found) to avoid an exception being thrown.
Other uses of find are usually replaced with things like this:
Model.all
Model.first
find_by is used as a helper when you're searching for information within a column, and it maps to such with naming conventions. For instance, if you have a column named name in your database, you'd use the following syntax:
Model.find_by(name: "Bob")
.where is more of a catch all that lets you use a bit more complex logic for when the conventional helpers won't do, and it returns an array of items that match your conditions (or an empty array otherwise).
Model.find
1- Parameter: ID of the object to find.
2- If found: It returns the object (One object only).
3- If not found: raises an ActiveRecord::RecordNotFound exception.
Model.find_by
1- Parameter: key/value
Example:
User.find_by name: 'John', email: 'john#doe.com'
2- If found: It returns the object.
3- If not found: returns nil.
Note: If you want it to raise ActiveRecord::RecordNotFound use find_by!
Model.where
1- Parameter: same as find_by
2- If found: It returns ActiveRecord::Relation containing one or more records matching the parameters.
3- If not found: It return an Empty ActiveRecord::Relation.
There is a difference between find and find_by in that find will return an error if not found, whereas find_by will return null.
Sometimes it is easier to read if you have a method like find_by email: "haha", as opposed to .where(email: some_params).first.
Since Rails 4 you can do:
User.find_by(name: 'Bob')
which is the equivalent find_by_name in Rails 3.
Use #where when #find and #find_by are not enough.
The accepted answer generally covers it all, but I'd like to add something,
just incase you are planning to work with the model in a way like updating, and you are retrieving a single record(whose id you do not know), Then find_by is the way to go, because it retrieves the record and does not put it in an array
irb(main):037:0> #kit = Kit.find_by(number: "3456")
Kit Load (0.9ms) SELECT "kits".* FROM "kits" WHERE "kits"."number" =
'3456' LIMIT 1
=> #<Kit id: 1, number: "3456", created_at: "2015-05-12 06:10:56",
updated_at: "2015-05-12 06:10:56", job_id: nil>
irb(main):038:0> #kit.update(job_id: 2)
(0.2ms) BEGIN Kit Exists (0.4ms) SELECT 1 AS one FROM "kits" WHERE
("kits"."number" = '3456' AND "kits"."id" != 1) LIMIT 1 SQL (0.5ms)
UPDATE "kits" SET "job_id" = $1, "updated_at" = $2 WHERE "kits"."id" =
1 [["job_id", 2], ["updated_at", Tue, 12 May 2015 07:16:58 UTC +00:00]]
(0.6ms) COMMIT => true
but if you use where then you can not update it directly
irb(main):039:0> #kit = Kit.where(number: "3456")
Kit Load (1.2ms) SELECT "kits".* FROM "kits" WHERE "kits"."number" =
'3456' => #<ActiveRecord::Relation [#<Kit id: 1, number: "3456",
created_at: "2015-05-12 06:10:56", updated_at: "2015-05-12 07:16:58",
job_id: 2>]>
irb(main):040:0> #kit.update(job_id: 3)
ArgumentError: wrong number of arguments (1 for 2)
in such a case you would have to specify it like this
irb(main):043:0> #kit[0].update(job_id: 3)
(0.2ms) BEGIN Kit Exists (0.6ms) SELECT 1 AS one FROM "kits" WHERE
("kits"."number" = '3456' AND "kits"."id" != 1) LIMIT 1 SQL (0.6ms)
UPDATE "kits" SET "job_id" = $1, "updated_at" = $2 WHERE "kits"."id" = 1
[["job_id", 3], ["updated_at", Tue, 12 May 2015 07:28:04 UTC +00:00]]
(0.5ms) COMMIT => true
Apart from accepted answer, following is also valid
Model.find() can accept array of ids, and will return all records which matches.
Model.find_by_id(123) also accept array but will only process first id value present in array
Model.find([1,2,3])
Model.find_by_id([1,2,3])
The answers given so far are all OK.
However, one interesting difference is that Model.find searches by id; if found, it returns a Model object (just a single record) but throws an ActiveRecord::RecordNotFound otherwise.
Model.find_by is very similar to Model.find and lets you search any column or group of columns in your database but it returns nil if no record matches the search.
Model.where on the other hand returns a Model::ActiveRecord_Relation object which is just like an array containing all the records that match the search. If no record was found, it returns an empty Model::ActiveRecord_Relation object.
I hope these would help you in deciding which to use at any point in time.
Suppose I have a model User
User.find(id)
Returns a row where primary key = id. The return type will be User object.
User.find_by(email:"abc#xyz.com")
Returns first row with matching attribute or email in this case. Return type will be User object again.
Note :- User.find_by(email: "abc#xyz.com") is similar to User.find_by_email("abc#xyz.com")
User.where(project_id:1)
Returns all users in users table where attribute matches.
Here return type will be ActiveRecord::Relation object. ActiveRecord::Relation class includes Ruby's Enumerable module so you can use it's object like an array and traverse on it.
Both #2s in your lists are being deprecated. You can still use find(params[:id]) though.
Generally, where() works in most situations.
Here's a great post: https://web.archive.org/web/20150206131559/http://m.onkey.org/active-record-query-interface
The best part of working with any open source technology is that you can inspect length and breadth of it.
Checkout this link
find_by ~> Finds the first record matching the specified conditions. There is no implied ordering so if order matters, you should specify it yourself. If no record is found, returns nil.
find ~> Finds the first record matching the specified conditions , but if no record is found, it raises an exception but that is done deliberately.
Do checkout the above link, it has all the explanation and use cases for the following two functions.
I will personally recommend using
where(< columnname> => < columnvalue>)
How do I define a model attribute as an expression of another attribute?
Example:
Class Home < ActiveRecord::Base
attr_accessible :address, :phone_number
Now I want to be able to return an attribute like :area_code, which would be an sql expression like "substr(phone_number, 1,3)".
I also want to be able to use the expression / attribute in a group by query for a report.
This seems to perform the query, but does not return an object with named attributes, so how do I use it in a view?
Rails Console:
#ac = Home.group("substr(phone_number, 1,3)").count
=> #<OrderedHash {"307"=>3, "515"=>1}>
I also expected this to work, but not sure what kind of object it is returning:
#test = Home.select("substr(phone_number, 1,3) as area_code, count(*) as c").group("substr(phone_number, 1,3)")
=> [#<Home>, #<Home>]
To expand on the last example. Here it is with Active Record logging turned on:
>Home.select("substr(phone_number, 1,3) as area_code, count(*) as c").group("substr(phone_number, 1,3)")
Output:
Home Load (0.3ms) SELECT substr(phone_number, 1,3) as area_code, count(*) as c FROM "homes" GROUP BY substr(phone_number, 1,3)
=> [#<Home>, #<Home>]
So it is executing the query I want, but giving me an unexpected data object. Shouldn't I get something like this?
[ #<area_code: "307", c: 3>, #<area_code: "515", c: 1> ]
you cannot access to substr(...) because it is not an attribute of the initialized record object.
See : http://guides.rubyonrails.org/active_record_querying.html "selecting specific fields"
you can workaround this this way :
#test = Home.select("substr(phone_number, 1,3) as phone_number").group(:phone_number)
... but some might find it a bit hackish. Moreover, when you use select, the records will be read-only, so be careful.
if you need the count, just add .count at the end of the chain, but you will get a hash as you already had. But isn't that all you need ? what is your purpose ?
You can also use an area_code column that will be filled using callbacks on create and update, so you can index this column ; your query will run fast on read, though it will be slower on insertion.
How do you do an OR query in Rails 3 ActiveRecord. All the examples I find just have AND queries.
Edit: OR method is available since Rails 5. See ActiveRecord::QueryMethods
If you want to use an OR operator on one column's value, you can pass an array to .where and ActiveRecord will use IN(value,other_value):
Model.where(:column => ["value", "other_value"]
outputs:
SELECT `table_name`.* FROM `table_name` WHERE `table_name`.`column` IN ('value', 'other_value')
This should achieve the equivalent of an OR on a single column
in Rails 3, it should be
Model.where("column = ? or other_column = ?", value, other_value)
This also includes raw sql but I dont think there is a way in ActiveRecord to do OR operation. Your question is not a noob question.
Rails 5 added or, so this is easier now in an app with Rails version greater than 5:
Model.where(column: value).or(Model.where(other_column: other_value)
this handles nil values as well
Use ARel
t = Post.arel_table
results = Post.where(
t[:author].eq("Someone").
or(t[:title].matches("%something%"))
)
The resulting SQL:
ree-1.8.7-2010.02 > puts Post.where(t[:author].eq("Someone").or(t[:title].matches("%something%"))).to_sql
SELECT "posts".* FROM "posts" WHERE (("posts"."author" = 'Someone' OR "posts"."title" LIKE '%something%'))
An updated version of Rails/ActiveRecord may support this syntax natively. It would look similar to:
Foo.where(foo: 'bar').or.where(bar: 'bar')
As noted in this pull request https://github.com/rails/rails/pull/9052
For now, simply sticking with the following works great:
Foo.where('foo= ? OR bar= ?', 'bar', 'bar')
Update: According to https://github.com/rails/rails/pull/16052 the or feature will be available in Rails 5
Update: Feature has been merged to Rails 5 branch
Rails has recently added this into ActiveRecord. It looks to be released in Rails 5. Committed to master already:
https://github.com/rails/rails/commit/9e42cf019f2417473e7dcbfcb885709fa2709f89
Post.where(column: 'something').or(Post.where(other: 'else'))
# => SELECT * FROM posts WHERE (column = 'something') OR (other = 'else)
Rails 5 comes with an or method. (link to documentation)
This method accepts an ActiveRecord::Relation object. eg:
User.where(first_name: 'James').or(User.where(last_name: 'Scott'))
If you want to use arrays as arguments, the following code works in Rails 4:
query = Order.where(uuid: uuids, id: ids)
Order.where(query.where_values.map(&:to_sql).join(" OR "))
#=> Order Load (0.7ms) SELECT "orders".* FROM "orders" WHERE ("orders"."uuid" IN ('5459eed8350e1b472bfee48375034103', '21313213jkads', '43ujrefdk2384us') OR "orders"."id" IN (2, 3, 4))
More information: OR queries with arrays as arguments in Rails 4.
The MetaWhere plugin is completely amazing.
Easily mix OR's and AND's, join conditions on any association, and even specify OUTER JOIN's!
Post.where({sharing_level: Post::Sharing[:everyone]} | ({sharing_level: Post::Sharing[:friends]} & {user: {followers: current_user} }).joins(:user.outer => :followers.outer}
Just add an OR in the conditions
Model.find(:all, :conditions => ["column = ? OR other_column = ?",value, other_value])
With rails + arel, a more clear way:
# Table name: messages
#
# sender_id: integer
# recipient_id: integer
# content: text
class Message < ActiveRecord::Base
scope :by_participant, ->(user_id) do
left = arel_table[:sender_id].eq(user_id)
right = arel_table[:recipient_id].eq(user_id)
where(Arel::Nodes::Or.new(left, right))
end
end
Produces:
$ Message.by_participant(User.first.id).to_sql
=> SELECT `messages`.*
FROM `messages`
WHERE `messages`.`sender_id` = 1
OR `messages`.`recipient_id` = 1
You could do it like:
Person.where("name = ? OR age = ?", 'Pearl', 24)
or more elegant, install rails_or gem and do it like:
Person.where(:name => 'Pearl').or(:age => 24)
I just extracted this plugin from client work that lets you combine scopes with .or., ex. Post.published.or.authored_by(current_user). Squeel (newer implementation of MetaSearch) is also great, but doesn't let you OR scopes, so query logic can get a bit redundant.
I'd like to add this is a solution to search multiple attributes of an ActiveRecord. Since
.where(A: param[:A], B: param[:B])
will search for A and B.
Using the activerecord_any_of gem, you can write
Book.where.any_of(Book.where(:author => 'Poe'), Book.where(:author => 'Hemingway')