“exto.Schema.Metadata”的目的是什么(i、 例如,`\u meta\`字段)

Ecto Schema 和 Changeset 仅用于验证,而不将任何内容持久化到数据库并尝试确定是否应该使用 Ecto.Schema.schema/2 或 Ecto.Schema.embedded_schema/1 嵌入式架构不需要源名称,也不包含元数据字段。 "

embedded_schema/1 ,效果很好,但这让我很疑惑 这个 Ecto.Schema.Metadata docs 对澄清这一点没有多大帮助:

字段包括:

• state—结构生命周期中的状态,其中一个:build,:loaded,
• source—查询旁架构的源 前缀,默认为{nil,“source”}
• context—由 数据库

正在搜索“ 元 Ecto.Schema docs ,在上面引用的 嵌入式架构/1 .

更新

the updated Metadata docs

 Stores metadata of a struct.  

  ## State

  The state of the schema is stored in the `:state` 
  field and allows following values:

    * `:built` - the struct was constructed in 
                 memory and is not persisted
                 to database yet;

    * `:loaded` - the struct was loaded from database 
                  and represents persisted data;

    * `:deleted` - the struct was deleted and no longer
                   represents persisted data.

  ## Source
  The `:source` tracks the (table or collection) where
  the struct is or should be persisted to.

  ## Prefix
  Tracks the source prefix in the data storage.

  ## Context
  The `:context` field represents additional state some 
  databases require for proper updates of data. It is 
  not used by the built-in adapters of `Ecto.Adapters.Postres` 
  and `Ecto.Adapters.MySQL`.

  ## Schema
  The `:schema` field refers the module name for the 
  schema this metadata belongs to.

( The updated Schema docs 同时解决我的上述困境:

  An Ecto schema is used to map any data source into an Elixir struct.
  The definition of the schema is possible through two main APIs:
  `schema/2` and `embedded_schema/1`.

  `schema/2` is typically used to map data from a persisted source,
  usually a database table, into Elixir structs and vice-versa. For
  this reason, the first argument of `schema/2` is the source (table)
  name. Structs defined with `schema/2` also contain a `__meta__` field
  with metadata holding the status of the struct, for example, if it
  has been built, loaded or deleted.

  On the other hand, `embedded_schema/1` is used for defining schemas
  that are embedded in other schemas or only exist in-memory. For example,
  you can use such schemas to receive data from a command line interface
  and validate it, without ever persisting it elsewhere. Such structs
  do not contain a `__meta__` field, as they are never persisted.

)