I know in rails model there is a method called validate_uniqueness_of.
I would like to understand how does Rails knows that a specific record is duplicated? What if the user chose the same options or data from yesterday or last last week?
Have you checked out find_or_create_by? This allows you to either find a record with certain atteributes, or create a new one based on the data.
So for instance. consider the following:
u = User.find_or_create_by(name:"Test", email:"test#test.com")
# while later
u = User.find_or_create_by(name:"Test", email:"test#test.com")
This will effectively be the same record, the second call will only query the record, instead of creating a new one.
Related
In my sample ruby apps a query like that
#ip = User.where("id = ?",#user[:user_id]).select('ip').first
returns
{"id":null,"ip":"127.0.0.1"}
And i don't want it to return id, although the id is 1, it returns is as null.
PS: it wont return id:null if i mentioned id in select like .select('id,ip')
Any help? i want just ip at return.
You may want to try pluck instead, which will return only the value you want.
ip = Model.where(conditions).pluck(:ip).first
You're misunderstanding what select does. Check out the Ruby docs to get a better understanding on how that method is used.
If all you're wanting to do is return the ip attribute from your User model based on finding a record with an id, all you need is this:
User.find(#user[:user_id]).ip
Notice that I'm using find and not where. As id should always be a unique value, there's no need to use a combination of where and first to get the single record you're looking for.
ALSO
Based on your example, I'm assuming that your #user variable is an object that you created and not a instance of your User model, which is why you're accessing user_id instead of just id.
However, if it is an instance of your User model, then two things to keep in mind:
you'll want to access id, not user_id - and you also don't need to access it via #user[:id]. You can just do #user.id.
you don't need to find the record at all. If you already have the User object that you're trying to find, then you can just get the ip from the object itself - i.e. #user.ip.
If you've already got the instance of a user you care about, and the IP field isn't a join to another table, then simply pull it off of the instance.
#ip = #user.ip
There's no benefit to going back to the database for information that you already have.
I have a procedure which receives two models, one which already exists, and another one which holds new attributes which I want to merge in the first one.
Since other parts of the program are holding the same reference to the new model, I can't just operate on the existing one. Therefor I do the following:
def merge(new_model, existing_model)
new_model.attributes = existing_model.attributes.merge(new_model.attributes)
new_model.id = existing_model.id
end
Now the new_model is being saved which gives me the uniqueness erorr (even though it's technically the same model). I also tried using the reload method, but that yields the same result.
Background:
The method above is run in a before_add callback on an association. I want to be able to call update on a model (with nested associations) without having to specify IDs of the nested models. This update is supposed to merge some associations, which is why I try to do the whole merge thing above.
You can't set the id of a model and then save the record expecting the id to be set since the id is the primary key of the database. So you are actually creating a whole new record and, thus, the uniqueness validation error. So you'll need to think of some other design to accomplish what you are wanting. It may help to know that what you are trying to do sounds similar to a deep_dup, except that ActiveRecord doesn't define this method (but Hash does).
I am putting together my first Sproutcore app. I have a simple model, a controller and a view. When I add a new record using store.createRecord() or .createRecords() they get added to the store, the controller and the view.
However, when I try to add new records via store.loadRecords() (from a remote source) from the response (e.g. [{"name":"test1"},{"name":"test2"},{"name":"test3"}]), only the last of the records (test3 in this case) ends up in the store. How can I change store.loadRecords() to actually add all the records?
Found the problem: I did not define the primaryKey in the Model. "primaryKey: 'id'," As easy as that.
I'm new to rails.
Is there an easy way in active record to pass it a hash of data and if the record exists, update it, and if it doesn't, create it?
data = {}
data["my_id"] = 356345
data["description"] = "test123"
w = Descriptions.new(data)
Ideally if I ran the above it would only ever have 1 record, not multiple records each time I ran it.
Assuming you ware wanting the "my_id" bit to be unique you can run
Descriptions.find_or_create_by_my_id(data["my_id"]).update_attributes(data)
An ActiveRecord object in Rails retains its identity in the ID parameter. If the ID is set, Rails will know to update the record in the database with that ID.
save is, in fact, the primary way to create, update, or in any way save an object to the database. Other methods like update_attributes are just sugar that use save at their core.
Yes,There are many good things you will get ModelName.find_or_create_by_name("Summer")
But If you pass Id in save method that will be update and if id is not passed it will create data.
Always, Primary Key in Rails should be "id" but you used "my_id" that may also be the problem.
#user = User.new
#user.id returns nil but i need to know it before i save. Is it possible ?
YES you can!
I had the same question and investigated the docs.
The ability to solve this question is very related to your database type in fact.
Oracle and Postgresql do have useful functions to easily solve this.
For MySQL(oracle) or SkySQL(open-source) it seems more complicated (but still possible). I would recommend you avoid using these (MySQL/SkySQL) databases if you need advanced database tools.
First you must try to avoid this situation as much as possible in your application design, as it is dangerous to play with IDs before they get saved.
There may be situation where you don't have any other choice:
For instance when two tables are referencing themselves and for security reason you don't allow DELETE or UPDATE on these tables.
When this is the case, you can use the (PostgreSQL, Oracle) database nextval function to generate the next ID number without actually inserting a new record.
Use it in conjunction with the find_by_sql rails method.
To do this with postgreSQL and Rails for instance, choose one of your rails models and add a class method (not an instance method!).
This is possible with the "self" word at the beginning of the method name.
self tells Ruby that this method is usable only by the class, not by its instance variables (the objects created with 'new').
My Rails model:
class MyToy < ActiveRecord::Base
...
def self.my_next_id_sequence
self.find_by_sql "SELECT nextval('my_toys_id_seq') AS my_next_id"
end
end
When you generate a table with a Rails migration, by default Rails automatically creates a column called id and sets it as the primary key's table. To ensure that you don't get any "duplicate primary key error", Rails automatically creates a sequence inside the database and applies it to the id column. For each new record (row) you insert in your table, the database will calculate by itself what will be the next id for your new record.
Rails names this sequence automatically with the table name append with "_id_seq".
The PostgreSQL nextval function must be applied to this sequence as explained here.
Now about find_by_sql, as explained here, it will create an array containing new objects instances of your class. Each of those objects will contain all the columns the SQL statement generates. Those columns will appear in each new object instance under the form of attributes. Even if those attributes don't exist in your class model !
As you wisely realized, our nextval function will only return a single value.
So find_by_sql will create an array containing a single object instance with a single attribute.
To make it easy to read the value of this very attribute, we will name the resulting SQL column with "my_next_id", so our attribute will have the same name.
So that's it. We can use our new method:
my_resulting_array = MyToy.my_next_id_sequence
my_toy_object = my_resulting_array[0]
my_next_id_value = my_toy_object.my_next_id
And use it to solve our dead lock situation :
my_dog = DogModel.create(:name => 'Dogy', :toy_id => my_next_id_value)
a_dog_toy = MyToy.new(:my_dog_id => my_dog.id)
a_dog_toy.id = my_next_id_value
a_dog_toy.save
Be aware that if you don't use your my_next_id_value this id number will be lost forever. (I mean, it won't be used by any record in the future).
The database doesn't wait on you to use it. If somewhere at any time, your application needs to insert a new record in your my_table_example (maybe at the same time as we are playing with my_next_id_sequence), the database will always assign an id number to this new record immediately following the one you generated with my_next_id_sequence, considering that your my_next_id_value is reserved.
This may lead to situations where the records in your my_table_example don't appear to be sorted by the time they were created.
No, you can't get the ID before saving. The ID number comes from the database but the database won't assign the ID until you call save. All this is assuming that you're using ActiveRecord of course.
I had a similar situation. I called the sequence using find_by_sql on my model which returns the model array. I got the id from the first object of the arry. something like below.
Class User < ActiveRecord::Base
set_primary_key 'user_id'
alias user_id= id=
def self.get_sequence_id
self.find_by_sql "select TEST_USER_ID_SEQ.nextval as contact_id from dual"
end
end
and on the class on which you reference the user model,
#users = User.get_sequence_id
user = users[0]
Normally the ID is filled from a database sequence automatically.
In rails you can use the after_create event, which gives you access to the object just after it has been saved (and thus it has the ID). This would cover most cases.
When using Oracle i had the case where I wanted to create the ID ourselves (and not use a sequence), and in this post i provide the details how i did that. In short the code:
# a small patch as proposed by the author of OracleEnhancedAdapter: http://blog.rayapps.com/2008/05/13/activerecord-oracle-enhanced-adapter/#comment-240
# if a ActiveRecord model has a sequence with name "autogenerated", the id will not be filled in from any sequence
ActiveRecord::ConnectionAdapters::OracleEnhancedAdapter.class_eval do
alias_method :orig_next_sequence_value, :next_sequence_value
def next_sequence_value(sequence_name)
if sequence_name == 'autogenerated'
# we assume id must have gotten a good value before insert!
id
else
orig_next_sequence_value(sequence_name)
end
end
end
while this solution is specific to Oracle-enhanced, i am assuming the other databases will have a similar method that you could redefine.
So, while it is definitely not advised and you want to be absolutely sure why you would not want to use an id generated by a sequence, if it is needed it is most definitely possible.
It is why I love ruby and Ruby on Rails! :)
In Oracle you can get your current sequence value with this query:
SELECT last_number FROM user_sequences where sequence_name='your_sequence_name';
So in your model class, you can put something like this:
class MyModel < ActiveRecord::Base
self.sequence_name = 'your_sequence_name'
def self.my_next_id_sequence
get_data = self.find_by_sql "SELECT last_number FROM user_sequences where sequence_name='your_sequence_name'"
get_data[0].last_number
end
end
And finally, in controller you can get this value with this:
my_sequence_number = MyModel.my_next_id_sequence
So, there is no need to get your next value by using NEXTVAL and you won't lose you ID.
What you could do is User.max(id). which will return the highest ID in the database, you could then add 1. This is not reliable, although might meet your needs.
Since Rails 5 you can simply call next_sequence_value
Note: For Oracle when self.sequence_name is set, requesting next sequence value creates side effect by incrementing sequence value