[ci skip][docs] Adds guide for Active Record Aggregations With Examples And References #55765
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shivabhusal
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| composed_of :price, | ||
| class_name: "Money", | ||
| mapping: [%w(price_cents amount), %w(price_currency currency)], | ||
| # mapping: {price_cents: :amount, price_currency: :currency}, # alternative syntax |
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I know the docs often use the array form, but I think the hash syntax is much nicer and clearer. Could we use that as the default?
| table columns. | ||
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| ```ruby | ||
| expensive_products = Product.where("price_cents > ?", 1000) |
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Shouldn't we be using the Money object here?
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yes we should. done!
| Since you cannot use aggregated attribute(like `price`) directly in database queries, | ||
| you need to use the underlying table columns(like `price_cents`) in scopes. |
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In the first paragraph you say
You can also use the aggregated attributes in scopes and validations
And here you say that we have to use the underlying table columns. I'm confused what is the aggregation doing here. It seems to only work on validations.
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made corrections
| composed_of :balance, class_name: "Money", mapping: { balance: :amount } | ||
| composed_of :address, mapping: { address_street: :street, address_city: :city } | ||
| composed_of :address, mapping: [%w(address_street street), %w(address_city city)] | ||
| composed_of :gps_location |
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Don't we need mappings other options for this?
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rails/activerecord/lib/active_record/aggregations.rb
Lines 225 to 236 in 529f933
Yes, it is also possible. Mapping is derived from part_id, i.e. :gps_location and other options are optional.
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| Other Option Examples | ||
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I think need a sentence before the code example.
| Here are some examples of value objects you might build using Active Record Aggregations in your app: | |
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accepted your suggestion
| Caveats | ||
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| ### Query with values in different units |
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This is not exclusive to units. Value objects are identified by their values, so if you're using a different value, it's a different object.
The same would happen with a Distance object with kilometers vs miles.
A possible solution would be keep the db unit constant (dollars, meters, etc) and perform conversions/compasissons at the class level
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I have added new descriptive example
| product.changed? # => true | ||
| product.changes_to_save # => {"price_cents"=>[1000, 2000], "price_currency"=>["USD", "EUR"]} | ||
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| product.price_changed? # => NoMethodError (no direct price_changed?) |
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Unrelated to this PR, but at first sight this seems doable. We could delegate methods back to the original model (if we have access to that)
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I will have a look later if we can make such changes
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Motivation / Background
While browsing the Active Record codebase, I came across the
Aggregationsmodule. I realized that, despite its usefulness, it isn’t currently documented in the Rails Guides. After confirming that no guide exists for this feature, I decided to add one so that developers can better understand and utilize Active Record Aggregations.Details
This pull request introduces a new guide for Active Record Aggregations, explaining how to use
composed_ofwith value objects through examples and caveats.Additionally, it updates the Rails Guides index and navigation menu to include this new document for easier discovery.
Suggestions, improvements, and feedback are very welcome.
Add Doc(Latest) Preview: https://shivabhusal-active-record-ag.rails-docs-preview.pages.dev/guides/active_record_aggregations
Checklist
Before submitting the PR make sure the following are checked: