We need to allow users to customize their entities like products... so my intention was to have a product table and a custom_product table with just the information the users are allowed to change.
When a client goes to the product I want to merge the information, means I want to merge the two tables - the custom overwrites the default Products table.
I know that in mysql there exists a ifnull(a.title, b.title) way but I was wondering if there is any nice and efficient way to solve this in Rails 4 with Active Record. Assume that the products and custom products table have just 2 columns, ID and TITLE
I think you can convert both objects to JSON and then handle their params as a hash, using the merge method:
class Product
end
class Customization
belongs_to :product
end
a = Product.find(...)
b = a.customization
c = JSON(a.to_json).merge(JSON(b.to_json).reject!{|k,v| v.nil?})
Therefore c will contain all params from Product eventually overridden by those in Customization which are not nil.
If you still want to use a Product object with hybrid values (taken from Customization) you can try this:
a.attributes = a.attributes.merge(b.attributes.reject!{|k,v| v.nil?})
In this case a will still be a Product instance. I would recommend to keep the same attributes in both models when doing this.
Related
I have a model called lists, which has a column called item_ids. item_ids is a JSON column (MySQL) and the column contains array of UUIDs, each referring to one item.
Now when someone creates a new list, I need to search whether there is an existing list with same set of UUIDs, and I want to do this search using query itself for faster response. Also use ActiveRecord querying as much as possible.
How do i achieve this?
item_ids = ["11E85378-CFE8-39F8-89DC-7086913CFD4B", "11E85354-304C-0664-9E81-0A281BE2CA42"]
v = List.new(item_ids: item_ids)
v.save!
Now, how do I check whether a list exists which has item ids exactly matches with that mentioned in query ? Following wont work.
list_count = List.where(item_ids: item_ids).count
Edit 1
List.where("JSON_CONTAINS(item_ids, ?) ", item_ids.to_json).count
This statement works, but it counts even if only one of the item matches. Looking for exact number of items.
Edit 2
List.where("JSON_CONTAINS( item_ids, ?) and JSON_LENGTH(item_ids) = ?", item_ids.to_json, item_ids.size).count
Looks like this is working
You can implement a has many relation between lists and items and then access like this.
List.includes(:item).where('items.id in (?)',item_ids)
To implement has_many relation:
http://guides.rubyonrails.org/association_basics.html#the-has-many-through-association
I've been trying to implement an authorization layer on top of ActiveRecord. Let me explain how that is supposed to work.
Databases
Consider a database table Invoices with the following fields
InvoiceId
CustomerId
... other fields
There will be an auxiliary table InvoicePrivileges with the fields
ObjectId (referring to an invoice id)
SubjectId (referring to a customer id in this case)
Subject type (to handle multiple kinds of users - customer, admin, operator, etc)
Read (boolean)
Write (boolean)
Authorization checks
To be able to read an invoice, the entity attempting to read the row or set of rows must have a set of entries in the InvoicePrivileges table (where InvoicePrivileges.object_id refers to an InvoiceId) with InvoicePrivileges.read = true.
Example, a query to fetch a bunch of invoices from the DB
SELECT invoice.*
FROM Invoices invoice
LEFT JOIN InvoicePrivileges privilege
ON invoice.invoice_id = privilege.object_id
AND privilege.subject_id = <user_id>
AND privilege.subject_type = <user_type>
WHERE privilege.read = TRUE;
The same condition applies when trying to update an invoice, except the last WHERE condition becomes WHERE privilege.write = true.
Implementation
I can use the Arel library to create these constraints with ease. However, where do I implement these methods in such a way that all ActiveRecord save and update actions include these constraints?
I don't mind writing a bit of code to enable this. I'm looking for pointers as to how best to go about it.
Create a gem and require it after ActiveRecord gem. In your gem open up ActiveRecord classes and override the interested methods.
module ActiveRecord
class Base
def save(*)
if(authorised?)
super
else
raise NotAuthorisedError.new("Your meaningful message!")
end
end
end
end
The original code from Rails source is in Persistence class. All persistence methods usually use create_or_update method internally. So, you might consider overriding that method instead. But, you need to look through the code and see if that's a good idea.
I'm learning sqlalchemy and not sure if I grasp it fully yet(I'm more used to writing queries by hand but I like the idea of abstracting the queries and getting objects). I'm going through the tutorial and trying to apply it to my code and ran into this part when defining a model:
def __repr__(self):
return "<User('%s','%s', '%s')>" % (self.name, self.fullname, self.password)
Its useful because I can just search for a username and get only the info about the user that I want but is there a way to either have multiple of these type of views that I can call? or am I using it wrong and should be writing a specific query for getting different data for different views?
Some context to why I'm asking my site has different templates, and most pages will just need the usersname, first/last name but some pages will require things like twitter or Facebook urls(also fields in the model).
First of all, __repr__ is not a view, so if you have a simple model User with defined columns, and you query for a User, all the columns will get loaded from the database, and not only those used in __repr__.
Lets take model Book (from the example refered to later) as a basis:
class Book(Base):
book_id = Column(Integer, primary_key=True)
title = Column(String(200), nullable=False)
summary = Column(String(2000))
excerpt = Column(Text)
photo = Column(Binary)
The first option to skip loading some columns is to use Deferred Column Loading:
class Book(Base):
# ...
excerpt = deferred(Column(Text))
photo = deferred(Column(Binary))
In this case when you execute query session.query(Book).get(1), the photo and excerpt columns will not be loaded until accessed from the code, at which point another query against the database will be executed to load the missing data.
But if you know before you query for the Book that you need the column photo immediately, you can still override the deferred behavior with undefer option: query = session.query(Book).options(undefer('photo')).get(1).
Basically, the suggestion here is to defer all the columns (in your case: except username, password etc) and in each use case (view) override with undefer those you know you need for that particular view. Please also see the group parameter of deferred, so that you can group the attributes by use case (view).
Another way would be to query only some columns, but in this case you are getting the tuple instance instead of the model instance (in your case User), so it is potentially OK for form filling, but not so good for model validation: session.query(Book.id, Book.title).all()
Suppose I have 3 tables in sqlalchemy. Users, Roles and UserRoles defined in declarative way. How would one suggest on doing something like this:
user = Users.query.get(1) # get user with id = 1
user_roles = user.roles.query.limit(10).all()
Currently, if I want to get the user roles I have to query any of the 3 tables and perform the joins in order to get the expected results. Calling directly user.roles brings a list of items that I cannot filter or limit so it's not very helpful. Joining things is not very helpful either since I'm trying to make a rest interface with requests such as:
localhost/users/1/roles so just by that query I need to be able to do Users.query.get(1).roles.limit(10) etc etc which really should 'smart up' my rest interface without too much bloated code and if conditionals and without having to know which table to join on what. Users model already has the roles as a relationship property so why can't I simply query on a relationship property like I do with normal models?
Simply use Dynamic Relationship Loaders. Code below verbatim from the documentation linked to above:
class User(Base):
__tablename__ = 'user'
posts = relationship(Post, lazy="dynamic")
jack = session.query(User).get(id)
# filter Jack's blog posts
posts = jack.posts.filter(Post.headline=='this is a post')
# apply array slices
posts = jack.posts[5:20]
I am currently evaluating SQLAlchemy for a project. Here is my schema:
a LANGUAGE table, with a row for each language supported
a TRANSLATION table with (ID, LANGUAGE_ID, STR)
various tables will, instead of storing text, store TRANSLATION_IDs, for example, BOOK(ID, TITLE_TRANSLATION_ID, ABSTRACT_TRANSLATION_ID)
Now, assuming each request has the current language ID available (for example, through a thread variable...), I would need SQLAlchemy to automatically join the TRANSLATION table, and thus have text fields in the current language. Something like:
class Book(Base):
id = Column(Integer, primary_key=True)
title = TranslatableText()
abstract = TranslatableText()
When retrieving, the ORM would automatically join to the TRANSLATION table with the current language ID, and my_book.title would give me the title in the current language.
I also need this to work across relations: if a class contains foreign keys to other classes that also contain translatable text fields, I would ideally like those to be retrieved too.
Lastly, I would also need to be able to get to the TRANSLATION_ID for each field, for example through my_book.title_translation_id.
I am not expecting a complete solution, but I'd like to know if something like this is feasible, and where to start.
You have to use the concept of http://docs.sqlalchemy.org/en/latest/orm/extensions/declarative.html#mixin-and-custom-base-classes
Create one top level class and write some funciton like read, write and create. Always call that function to create or read data from the database.
If you dont want to implement the mixin classes then also you can use event http://docs.sqlalchemy.org/en/latest/orm/events.html#sqlalchemy.orm.events.MapperEvents.translate_row