I have a table named subs which has many articles. The articles table has a timestamp column called published.
Sub.select( "subs.*,MAX(articles.published) published").joins("LEFT OUTER JOIN articles ON subs.id=articles.sub_id").group("subs.id").first.published.class
=> String
Article.select("max(published) published").group("id").first.published.class
=> ActiveSupport::TimeWithZone
I want to get an ActiveSupport::TimeWithZone object back from the first query.
Rails 3
Rails determines how to type cast attributes based on their database column definitions. For example, say you have a created_at method on your Sub model. When a record is loaded read_attribute is used (ActiveRecord::AttributeMethods::Read). This uses type_cast_attribute which determines how to cast the value based on the column info. For example, if you are using PostgreSQL it may use:
Sub.columns.detect { |c| c.name == "created_at" }.type_cast_code("v")
=> "ActiveRecord::ConnectionAdapters::PostgreSQLColumn.string_to_time(v)"
But Rails doesn't know what to do with columns that aren't on the Sub model. So it just gives back a String. If you need to work with a ActiveSupport::TimeWithZone object, you can cast the value with:
published = Sub.select( "subs.*,MAX(articles.published) published").joins("LEFT OUTER JOIN articles ON subs.id=articles.sub_id").group("subs.id").first.published
published.present? ? Time.zone.parse(published) : nil
Rails 4
In Rails 4, Rails is smarter about this kind of type-casting. When the SQL is executed, ActiveRecord::Result is created and the column_types are passed to the initializer. In your example Sub.select query, the published column would be cast as a Time object.
Related
I have a cosmos db collection. I need to query all documents and return them in order of creation date. Creation date is a defined field but for historical reason it is in string format as MM/dd/yyyy. For example: 02/09/2019. If I just order by this string, the result is chaos.
I am using linq lambda to write my query in webapi. I have tried to parse the string and try to convert the string. Both returned "method not supported".
Here is my query:
var query = Client.CreateDocumentQuery<MyModel>(CollectionLink)
.Where(f => f.ModelType == typeof(MyModel).Name.ToLower() && f.Language == getMyModelsRequestModel.Language )
.OrderByDescending(f => f.CreationDate)
.AsDocumentQuery();
Appreciate for any advice. Thanks. It will be huge effort to go back and modify the format of the field (which affects many other things). I wish to avoid it if possible.
Chen Wang.Since the order by does not support derived values or sub query(link),so you need to sort the derived values by yourself i think.
You could construct the MM/dd/yyyy to yyyymmdd by UDF in cosmos db.
udf:
function getValue(datetime){
return datetime.substring(6,10)+datetime.substring(0,2)+datetime.substring(3,5);
}
sql:
SELECT udf.getValue(c.time) as time from c
Then you could sort the array by property value of class in c# code.Please follow this case:How to sort an array containing class objects by a property value of a class instance?
I would like to join two query result.
First one is
Gig.where(id:gigsInRadioIDS)
When I convert result to json I get this result
[{"id":1,"address":"test1"},{"id":2,"address":"test2"}
Second is.
Slot.where(status:"available").where(Sequel.lit('("from" > ?) AND ("to" < ?)', fromdate, todate))
when I convert result to json I get this result
[{"id":15,"status":"available","gig_id":1}]
What I want is to inner join to result
so I hope to get this result(I abbreviated some non related snippet)
[{"id":15,"status":"available","gig_id":1,"id":1,"address":"test1"}]
What I have tried is
Gig.where(id:gigsInRadioIDS).as(:tb_gig).join(Slot.where(status:"available").where(Sequel.lit('("from" > ?) AND ("to" < ?)', fromdate, todate)), gig_id: :id)
And I got this error
Sequel::DatabaseError - PG::AmbiguousColumn: ERROR: column reference "id" is ambiguous
LINE 1: ...) AS "t1" ON ("t1"."gig_id" = "gigs"."id") WHERE ("id" IN (2...
Thanks for reading this complex code.
Any news will be big help. Thanks.
There are a bunch of ways to approach it. It looks like you are querying Slots with some Gigs data mixed in, so you may want to start with your Slot model. The regular join syntax is a little easier to understand and makes it easier to select columns from both tables (i.e. instead of WHERE fk IN (..)). As a bonus, you can mix your gig_id filter into the JOIN clause. Finally, you don't need to use Sequel.lit to do greater than / less than in your WHERE clause, and you should be explicit about the columns you want to select.
Here's how I would write it:
Slot.join(:gigs, [[:id, :gig_id], [:id, gigsInRadioIDS]])
.where(status: 'available') { (from() > fromdate) & (to() < todate) }
.select(Sequel[:slots][:id].as(:slot_id), :status, :gig_id, :address)
Getting .all of the records and outputting JSON should yield something like:
[{"slot_id":15,"status":"available","gig_id":1,"address":"test1"}]
Note the Sequel[:table_name][:column_name] syntax. This is the new style of fully-qualifying identifiers in Sequel 4.49+. (In past versions of Sequel, it would have been written like :table_name__column_name, but that syntax is now deprecated.)
Your where(id:gigsInRadioIDS) translates into WHERE ("id" IN (...)), and since both gigs and slots have an "id" column, the database doesn't know which id you want.
You need to explicitly specify the table with where{{gigs[:id] => gigsInRadioIDS}}
Querying with Sequel
When I try to run the following code, DataMapper calls for 3 queries in just these two lines. Can anyone explain why it would do this?
#u = User.first(:uid => 1, :fields => [:uid, :name])
json #u
This calls the following queries:
SELECT "uid", "name" FROM "users" WHERE "uid" = 1 ORDER BY "uid" LIMIT 1
SELECT "uid", "email" FROM "users" WHERE "uid" = 1 ORDER BY "uid"
SELECT "uid", "accesstoken" FROM "users" WHERE "uid" = 1 ORDER BY "uid"
It is worth noting that datamapper has a validation on name for being => unique
Also, the accesstoken is lazily loaded so it should only be queried when asked for specifically, which must be happening when serializing it to a json object.
EDIT:
I have added my model class for clarification. I just want one query made for the uid and name without having to extract them individually from the object. Maybe this is the only way?
property :uid, Serial
property :name, String
property :email, String
property :accesstoken, Text
ANSWER:
Use the dm-serializer gem that has this support built-in
https://github.com/datamapper/dm-serializer
The first query is invoked by your User.first... call. Notice the fields it's selecting are what you requested - uid and name
The second and third queries are getting run in the json serialization, as it's lazy loading each property you didn't already load.
So you either need to do a custom serialization to only output uid and name for your users, or you should just remove the field selection from your initial query so it all gets loaded at once.
Update:
To do a custom serialization with datamapper, you can use the dm-serializer gem https://github.com/datamapper/dm-serializer and call #u.to_json(only: [:uid, :name])
Alternatively in this simple case you could just build the serialized object you want yourself, for which there are many examples: Rails3: Take controll over generated JSON (to_json with datamapper ORM)
I have two models with the appropriate foreign key created in the people table:
class Person < ActiveRecord::Base
belongs_to :family
class Family < ActiveRecord::Base
has_many :people
If I do the following I get an object - #family_members - as an instance variable and I have no problems:
#family_members = Family.find(1)
I can access the 'child' people table fields easily in my view:
#family_members.people.first_name
However, if I use the arel way with "where" etc. I get an "ActiveRecord::Relation", not a normal object, which leaves me stumped as to how to access the same "first_name" field form the people table like I accessed above:
#family_members = Family.where(:id => 1)
or even
#family_members = Family.joins(:people).where(:id => 1)
(is the "joins" even required??)
I understand that using ".first" will cause the query to run:
#family_members = Family.where(:id => 1).first
But it returns an array, not an object, so if I use in my view:
#family_members.people.first_name
I get a "method 'people' unknown" error.
How can I access the 'first_name' field of the people table like I did with the object created by "find" but using an ActiveRecord relation?
* added information 7/15 ********
To clarify what I am looking for -- here is what I would have written if I were writing SQL instead of Arel:
SELECT f.home_phone, f.address, p.first_name, p.last_name, p.birthday
FROM families f INNER JOIN people p ON p.family.id = f.id WHERE family_id = 1
With that query's results loaded into a result set I could access:
myResultSet("home_phone") -- the home_phone from the families table
myResultSet("address") -- the address from the families table
myResultSet("first_name") -- the first_name from the people table
myResultSet("birthdate") -- the birthdate from the people table
If the two tables in the query have a same-named field I would just use "AS" to request one of the fields by another name.
I have used this kind of query/result set for many years in web apps and I am trying to deduce how to do the same in Rails and ActiveRecord.
#family_members.people.first_name shouldn't ever work so I'm surprised you find it working ... #family_members contains a Family object, #family_members.people is an array of Person objects.
The fact that you're calling it #family_members seems to make me think you're expecting it to be an array of Persons... in which case the correct code would be...
#family_members = Family.find(1).people # finds people in first Family object
If you expect #family_members to contain just the first family member, then...
#family_members = Family.find(1).people.first
If you want an array of first names of all family members, then...
#family_members = Family.find(1).people # finds people in 1st Family object
#family_members.map {|member| member.first_name} # array of first_name
#family_members = Family.find(1) and #family_members = Family.where(:id => 1) are functionally identical.. both retrieve the first Family object in the database in each case may contain zero, one, or multiple people.
Just to be clear, the "1" in all examples above refer to which Family object is retrieved, not which Person in the Family.
How can you run a Sequel migration that updates a newly added column with a value from the row?
The Sequel documentation shows how you can update the column with a static value:
self[:artists].update(:location=>'Sacramento')
What I need to do is update the new column with the value of the ID column:
something like:
self[:artists].each |artist| do
artist.update(:location => artist[:id])
end
But the above doesn't work and I have been unable to figure out how to get it to go.
Thanks!
artist in your loop is a Hash, so you are calling Hash#update, which just updates the Hash instance, it doesn't modify the database. That's why your loop doesn't appear to do anything.
I could explain how to make the loop work (using all instead of each and updating a dataset restricted to the matching primary key value), but since you are just assigning the value of one column to the value of another column for all rows, you can just do:
self[:artists].update(:location=>:id)
if you need update all rows of a table, because it is a new column that need be populate
artists = DB[:artists]
artists.update(:column_name => 'new value')
or if you need, update only a unique row into your migration file you can:
artists = DB[:artists]
artists.where(:id => 1).update(:column_name1 => 'new value1', :column_name2 => "other")