How get items from table ? I want get value from question column, using condition.
#result = Customers.where(:name => session[:username], :email => session[:useremail])
Now, I can get value from any column ? like this: #result.column_from_customers_table , right ?
This is a common mistake for beginners. The code you have returns an ActiveRecord::Relation object and doesn't actually connect to your db yet. In order to get a record you have to loop through each one of the results or call .first on it in order to get the first matching result
# returns an ActiveRecord::Relation object
#results = Customers.where(:name => session[:username], :email => session[:useremail])
# returns the first matching record
#object = #results.first
# then you can call the column names on #object
#object.name
#object.email
# looping through the results
#results.each do |object|
puts object.name
puts object.email
end
Related
I want to call the ActiveRecord method where with an array for a column. If the each item on the array doesn't exist, create the object. The closest method I found for this is first_or_create but this seems to be called only once, not for each time the record doesn't exist. Below is my example code-
hashtag_list = params[:message][:hashtag_primary]
#hashtags = Hashtag.where({:name => hashtag_list}).first_or_create do |hashtag|
hashtag.creator = current_user.id
end
Rails version- 4.2.1
I don't know a direct method, only a workaround
existing_tags = Hashtag.where({:name => hashtag_list}).pluck(:name)
not_existing_tags = hashtag_list - existing_tags
#hashtags = Hashtag.where({:name => existing_tags}).all
not_existing_tags.each do |tag|
#hashtags << Hashtag.new name: tag
end
#hashtags.each do |hashtag|
hashtag.creator = current_user.id
end
This is expected behavior of where + first_or_create method. Basically where(field: array) produces an SQL to find all records where field matches any item in the array. Than you have first_or_create method which takes the first record from results or creates a new one with escaped array value assigned to a field (so something like field: "[\"foo\", \"bar\"]" when used as where(field: %w(foo bar)).
If you want to create records for each hashtag from your list, you should iterate over it:
if #hashtag = Hashtag.where({:name => hashtag_list}).first
# do something if found the first one
else
hashtag_list.each do |hashtag|
# create an object
end
end
If you want to create missing hashtags even if the record is found, you can extract this to a private helper method with missing tags as the argument and re-write code as:
if #hashtags = Hashtag.where({:name => hashtag_list})
# do something if found
end
create_missing_hashtags(hashtag_list - #hashtags.pluck(:name))
1) I am grabbing some records for the DB in HAML to display, and the attributes method on each row returns a hash. The hash's keys are strings. Should I turn those keys into symbols? I am not sure the call to symbolize_keys is worth it. I.e.,
%td #{app['comment']}
or
%td #{app[:comment]
2) I am trying to symbolize the array of hashes I return, but it is not working:
rows = Comment.all(:order => 'created DESC')
result = rows.each_with_object([]) do |row, comments|
comments << row.attributes.symbolize_keys
end
Is it not actually pushing the symbolized hash into the comments array? I also tried symbolize_keys!, and that did not help. What am I doing wrong?
Since you're using Rails, you have access to HashWithIndifferentAccess so you can bypass your "strings or symbols" issue quite easily by allow both:
h = HashWithIndifferentAccess.new(some_model.attributes)
puts h['id'] # Gives you some_model.id
puts h[:id] # Also gives you some_model.id
Your each_with_object approach:
result = rows.each_with_object([]) do |row, comments|
comments << row.attributes.symbolize_keys
end
should work fine so I think your problem with that lies elsewhere.
Do you have a reason for using ActiveRecord::Base#attributes[your_attribute] instead of ActiveRecord::Base#your_attribute directly? You didn't mention a reason.
ActiveRecord::Base automatically sets up accessors for your database fields:
object = Model.new
object.your_column = "foo" # Writer
object.your_column # Reader
You should be able to use the reader in your views instead of accessing the value through ActiveRecord::Base#attributes.
Update:
I'm not sure if this is what confuses you.
Comment.find(:all) already retrieves all columns values for those rows in your database and stores them in your Comment objects (which we assign to #comments below). The values are already stored in your Comment objects, so you may already use them in your views as you please.
In your controller, if you have:
def index
#comments = Commend.find(:all) # Fetch columns and rows.
end
you can do this in your HAML view:
- #comments.each do |comment| # Iterate through array of Comment objects
%tr
%td= comment.comment # Use value for "comment" column.
you can add hook, which symbolizes keys after model load:
class YourModel < ApplicationRecord
after_initialize do |rec|
attributes["some_json_field"].symbolize_keys! if attributes.key? "some_json_field"
end
end
I wish I described this better, but it's the best I know how. I have two classes Cars and Colors. Each can have many of each other through a association class CarColors. The association is set up correctly I'm positive of this but I can't seem to get this to work:
#carlist = Cars.includes(:Colors).all
#carlist.colors
ERROR
#carlist[0].colors
WORKS
My question is how can I iterate over the #carlist without declaring a index as in the successful example? Below is a few things I have tried which also fail:
#carlist.each do |c|
c.colors
end
#carlist.each_with_index do |c,i|
c[i].colors
end
Your first example fails because Car.includes(:colors).all returns an array of cars, not a single car, so the following will fail, because #colors is not defined for the array
#cars = Car.includes(:colors).all
#cars.colors #=> NoMethodError, color is not defined for Array
The following will work, because the iterator will have an instance of car
#cars.each do |car|
puts car.colors # => Will print an array of color objects
end
each_with_index will work as well, but it is a bit different, as the first object
is the same as the each loop car object, the second object is the index
#cars.each_with_index do |car, index|
puts car.colors # => Will print an array of color objects
puts #cars[index].colors # => Will print an array of color objects
puts car == #cars[index] # => will print true
end
Is there a way to get the actual columns name with ActiveRecord?
When I call find_by_sql or select_all with a join, if there are columns with the same name, the first one get overridden:
select locations.*, s3_images.* from locations left join s3_images on s3_images.imageable_id = locations.id and s3_images.imageable_type = 'Location' limit 1
In the example above, I get the following:
#<Location id: 22, name: ...
>
Where id is that of the last s3_image. select_rows is the only thing that worked as expected:
Model.connection.select_rows("SELECT id,name FROM users") => [["1","amy"],["2","bob"],["3","cam"]]
I need to get the field names for the rows above.
This post gets close to what I want but looks outdated (fetch_fields doesn't seem to exist anymore How do you get the rows and the columns in the result of a query with ActiveRecord? )
The ActiveRecord join method creates multiple objects. I'm trying to achieve the same result "includes" would return but with a left join.
I am attempting to return a whole lot of results (and sometimes whole tables) this is why includes does not suit my needs.
Active Record provides a #column_names method that returns an array of column names.
Usage example: User.column_names
two options
Model.column_names
or
Model.columns.map(&:name)
Example
Model named Rabbit with columns name, age, on_facebook
Rabbit.column_names
Rabbit.columns.map(&:name)
returns
["id", "name", "age", "on_facebook", "created_at", "updated_at"]
This is just way active record's inspect method works: it only lists the column's from the model's table. The attributes are still there though
record.blah
will return the blah attribute, even if it is from another table. You can also use
record.attributes
to get a hash with all the attributes.
However, if you have multiple columns with the same name (e.g. both tables have an id column) then active record just mashes things together, ignoring the table name.You'll have to alias the column names to make them unique.
Okay I have been wanting to do something that's more efficient for a while.
Please note that for very few results, include works just fine. The code below works better when you have a lot of columns you'd like to join.
In order to make it easier to understand the code, I worked out an easy version first and expanded on it.
First method:
# takes a main array of ActiveRecord::Base objects
# converts it into a hash with the key being that object's id method call
# loop through the second array (arr)
# and call lamb (a lambda { |hash, itm| ) for each item in it. Gets called on the main
# hash and each itm in the second array
# i.e: You have Users who have multiple Pets
# You can call merge(User.all, Pet.all, lambda { |hash, pet| hash[pet.owner_id].pets << pet }
def merge(mainarray, arr, lamb)
hash = {}
mainarray.each do |i|
hash[i.id] = i.dup
end
arr.each do |i|
lamb.call(i, hash)
end
return hash.values
end
I then noticed that we can have "through" tables (nxm relationships)
merge_through! addresses this issue:
# this works for tables that have the equivalent of
# :through =>
# an example would be a location with keywords
# through locations_keywords
#
# the middletable should should return as id an array of the left and right ids
# the left table is the main table
# the lambda fn should store in the lefthash the value from the righthash
#
# if an array is passed instead of a lefthash or a righthash, they'll be conveniently converted
def merge_through!(lefthash, righthash, middletable, lamb)
if (lefthash.class == Array)
lhash = {}
lefthash.each do |i|
lhash[i.id] = i.dup
end
lefthash = lhash
end
if (righthash.class == Array)
rhash = {}
righthash.each do |i|
rhash[i.id] = i.dup
end
righthash = rhash
end
middletable.each do |i|
lamb.call(lefthash, righthash, i.id[0], i.id[1])
end
return lefthash
end
This is how I call it:
lambmerge = lambda do |lhash, rhash, lid, rid|
lhash[lid].keywords << rhash[rid]
end
Location.merge_through!(Location.all, Keyword.all, LocationsKeyword.all, lambmerge)
Now for the complete method (which makes use of merge_through)
# merges multiple arrays (or hashes) with the main array (or hash)
# each arr in the arrs is a hash, each must have
# a :value and a :proc
# the procs will be called on values and main hash
#
# :middletable will merge through the middle table if provided
# :value will contain the right table when :middletable is provided
#
def merge_multi!(mainarray, arrs)
hash = {}
if (mainarray.class == Hash)
hash = mainarray
elsif (mainarray.class == Array)
mainarray.each do |i|
hash[i.id] = i.dup
end
end
arrs.each do |h|
arr = h[:value]
proc = h[:proc]
if (h[:middletable])
middletable = h[:middletable]
merge_through!(hash, arr, middletable, proc)
else
arr.each do |i|
proc.call(i, hash)
end
end
end
return hash.values
end
Here's how I use my code:
def merge_multi_test()
merge_multi!(Location.all,
[
# each one location has many s3_images (one to many)
{ :value => S3Image.all,
:proc => lambda do |img, hash|
if (img.imageable_type == 'Location')
hash[img.imageable_id].s3_images << img
end
end
},
# each location has many LocationsKeywords. Keywords is the right table and LocationsKeyword is the middletable.
# (many to many)
{ :value => Keyword.all,
:middletable => LocationsKeyword.all,
:proc => lambda do |lhash, rhash, lid, rid|
lhash[lid].keywords << rhash[rid]
end
}
])
end
You can modify the code if you wish to lazy load attributes that are one to many (such as a City is to a Location) Basically, the code above won't work because you'll have to loop through the main hash and set the city from the second hash (There is no "city_id, location_id" table). You could reverse the City and Location to get all the locations in the city hash then extract back. I don't need that code yet so I skipped it =)
I'm doing this:
#snippets = Snippet.find :all, :conditions => { :user_id => session[:user_id] }
#snippets.each do |snippet|
snippet.tags.each do |tag|
#tags.push tag
end
end
But if a snippets has the same tag two time, it'll push the object twice.
I want to do something like if #tags.in_object(tag)[...]
Would it be possible? Thanks!
I think there are 2 ways to go about it to get a faster result.
1) Add a condition to your find statement ( in MySQL DISTINCT ). This will return only unique result. DBs in general do much better jobs than regular code at getting results.
2) Instead if testing each time with include, why don't you do uniq after you populate your array.
here is example code
ar = []
data = []
#get some radom sample data
100.times do
data << ((rand*10).to_i)
end
# populate your result array
# 3 ways to do it.
# 1) you can modify your original array with
data.uniq!
# 2) you can populate another array with your unique data
# this doesn't modify your original array
ar.flatten << data.uniq
# 3) you can run a loop if you want to do some sort of additional processing
data.each do |i|
i = i.to_s + "some text" # do whatever you need here
ar << i
end
Depending on the situation you may use either.
But running include on each item in the loop is not the fastest thing IMHO
Good luck
Another way would be to simply concat the #tags and snippet.tags arrays and then strip it of duplicates.
#snippets.each do |snippet|
#tags.concat(snippet.tags)
end
#tags.uniq!
I'm assuming #tags is an Array instance.
Array#include? tests if an object is already included in an array. This uses the == operator, which in ActiveRecord tests for the same instance or another instance of the same type having the same id.
Alternatively, you may be able to use a Set instead of an Array. This will guarantee that no duplicates get added, but is unordered.
You can probably add a group to the query:
Snippet.find :all, :conditions => { :user_id => session[:user_id] }, :group => "tag.name"
Group will depend on how your tag data works, of course.
Or use uniq:
#tags << snippet.tags.uniq