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Ecto - Coggle Diagram

- - - - Since the query will return all fields in MyApp.Post, when we convert it to a subquery, all of the fields from MyApp.Post will be available on the parent query, such as q.visits. In fact, Ecto will keep the schema properties across queries. For example, if you write q.field_that_does_not_exist, your Ecto query won't compile.
        https://hexdocs.pm/ecto/aggregates-and-subqueries.html
- - - - Creating a Blog site
        
        One post can have many Tags
        
        We want to be allow the user to flexibly insert tags
        
        "elixir, erlang, ecto" should translate into 3 tags, if they are new we should insert them
        
        put_assoc vs cast_assoc
        
        The cast_assoc/3 changeset function was designed to receive external parameters and compare them with the associated data in our structs.
        
        Reasons
        
        3 more items...
- - - - If parameter does not contain ID
        
        If there is an associated child with an ID and its ID is not given as parameter, the :on_replace callback for that association will be invoked (see the "On replace" section on the module documentation)
        
        If the parameter does not contain an ID, the parameter data will be passed to MyApp.Address.changeset/2 with a new struct and become an insert operation. We only consider the ID as not given if there is no "id" key or if its value is strictly nil
      - If parameter does contain an ID
        
        No associated child in preloaded data with matching ID
        
        The parameter data will be passed to MyApp.Address.changeset/2 with a new struct and become an insert operation
        
        Associated child in preloaded data with matching ID
        
        The parameter data will be passed to MyApp.Address.changeset/2 with the existing struct and become an update operation
- - - - on_conflict
        
        When inserting, if we try and insert when there's an existing entry, it will fail
        
        options
        
        that's because on_conflict is :raise by default
        
        :nothing
        
        If there is a conflict, do nothing (will no longer throw an error)
        
        documentation
        
        https://hexdocs.pm/ecto/Ecto.Repo.html#c:insert_all/3-upserts
- - - - https://hexdocs.pm/ecto/Ecto.Changeset.html#put_assoc/4
      - This function is used to work with associations as a whole. For example, if a Post has many Comments, it allows you to add, remove or change all comments at once.
      - giving us the ability to manipulate the data as we want in more flexible ways than casting does
    - - Structure of Params
        
        Requires the association come in as a list of maps
        
        Each map must include an id to know when to update, create, or delete
        
        https://hexdocs.pm/ecto/constraints-and-upserts.html#put_assoc-vs-cast_assoc
    - - cast_assoc
        
        When you want to change the parent struct and the child struct at the same time
        
        When you want to update existing data and insert new data at the same time
        
        User |> Repo.get!(id) |> Repo.preload(:addresses) # Only required when updating data |> Ecto.Changeset.cast(params, []) |> Ecto.Changeset.cast_assoc(:addresses, with: &MyApp.Address.changeset/2)