ruby-on-rails - 将 postgres ENUM 与 rails 一起使用会产生 `PG::DatatypeMismatch`

Question

尝试更新 Postgres ENUM 列的值会抛出以下异常:

ActiveRecord::StatementInvalid Exception: PG::DatatypeMismatch: ERROR: column "interesting_column" is of type interesting_thing but expression is of type integer

LINE 1: UPDATE "interesting_table" SET "interesting_column" = 0, "updated_a...

HINT: You will need to rewrite or cast the expression.

InterestingTable.first.update_attributes!(normal_column: 'food')
  # => perfectly fine
InterestingTable.first.update_attributes!(interesting_column: 'foo')
  # => above exception

这是创建表的迁移:

class CreateInterestingTables < ActiveRecord::Migration
  def up
    execute <<-SQL
      CREATE TYPE normal_thing AS ENUM ('food', 'water', 'shelter');
      CREATE TYPE interesting_thing AS ENUM ('foo', 'bar', 'baz');
    SQL

    create_table :interesting_tables do |t|
      t.column :normal_column, :normal_thing
      t.column :interesting_column, :interesting_thing
    end
  end

  def down
    drop_table :interesting_tables
    execute 'DROP TYPE normal_thing'
    execute 'DROP TYPE interesting_thing'
  end
end

Answer 1

问题在于，虽然该列在数据库中具有正确的类型，但 Active Record 会尝试将其解释为 integer。您可以通过运行来验证:

InterestingTable.columns
# => [#<ActiveRecord::ConnectionAdapters::PostgreSQLColumn:0x007f7567f82260
#      @coder=nil,
#      @default=nil,
#      @limit=nil,
#      @name="id",
#      @null=false,
#      @precision=nil,
#      @primary=true,
#      @scale=nil,
#      @sql_type="integer",
#      @type=:integer>,
#     #<ActiveRecord::ConnectionAdapters::PostgreSQLColumn:0x007f7568075690
#      @coder=nil,
#      @default=nil,
#      @limit=nil,
#      @name="normal_column",
#      @null=true,
#      @precision=nil,
#      @primary=false,
#      @scale=nil,
#      @sql_type="normal_thing",
#      @type=nil>,
#     #<ActiveRecord::ConnectionAdapters::PostgreSQLColumn:0x007f7568075668
#      @coder=nil,
#      @default=nil,
#      @limit=nil,
#      @name="interesting_column",
#      @null=true,
#      @precision=nil,
#      @primary=false,
#      @scale=nil,
#      @sql_type="interesting_thing",
#      @type=:integer>]

请注意第二列的类型是 nil，而最后一列的类型是 integer。如果您的字符串不是以数字开头，String#to_i 将返回 0，因此您会收到试图分配 0 的错误。

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但这是为什么呢？原因 - interesting_thing 包含子字符串 int，适配器认为它是一个 integer。这似乎是一个长期存在的错误，直到 rails 4.2 才得到修复。 The offending method.

---

可能的解决方案:

• 迁移到 rails 4.2+
• 将您的 ENUM 重命名为不匹配的名称
• Monkey 修补适配器。这是一个quick fix .