Question

我需要在数据库级别获取包含主键的列名。

Model.primary_key返回models_id列名，该列名不是在数据库级别上为主键。我仍然无法更改迁移或修改表。

我目前可以使用ActiveRecord::Base.connection.primary_key('table_name')通过MySqlAdapter来获取它

，但这不适用于具有复合主键的表。如果表包含复合主键，则它返回nil。

我可以通过编程方式实现此目的吗？

Answer 1

ActiveRecord不支持开箱即用的复合主键。

您需要安装composite_primary_keys gem，然后如果主键是复合键，ActiveRecord::Base.connection.primary_key('table_name')将返回一个列名数组。

Answer 2

执行查询：

<ScreenManagement>:
    MenuScreen:
        name: 'menu'
    CalculatorScreen:
        name: 'calculator'

<MenuScreen>:
    BoxLayout:
        Button:
            text: 'Goto Calculator'
            on_press: root.manager.current = 'calculator'
        Button:
            text: 'Quit'

<CalculatorScreen>:
    Calculator:

<CustButton@Button>:
    font_size: 35
    background_color: 0,0,0,0
    canvas.before:
        Color:
            rgba: (.4, .4, .4, 1) if self.state=='normal' else (0,.7,.7,1)
        RoundedRectangle:
            pos: self.pos
            size: self.size
            radius: [20, ]

<RawLayout@BoxLayout>:
    spacing: 8
    padding: 8
    size_hint: [1, .2]

<Calculator>:
    id: calculator
    rows: 10
    display: entry
    spacing: 1

    BoxLayout:
        size_hint: [1, .1]
        Label:
            text: 'Basic Calculator'
        Label:
            text: 'Made by Xrew'

    BoxLayout:
        padding: 10
        TextInput:
            id: entry
            spacing: 1
            padding: 5
            font_size: 32
            multiline: True
            focus: False
    #       background_color: 0, 0, 0, 1
    #       foreground_color: [1, 0, 1, 1]

    RawLayout:
        CustButton:
            text: '<'
            on_press: entry.text += self.text
        CustButton:
            text: '>'
            on_press: entry.text += self.text
        CustButton:
            text: '≈'
            on_press: entry.text += '=='

    RawLayout:
        orientation: 'horizontal'
        CustButton:
            text: '('
            on_press: entry.text += '('
        CustButton:
            text: ')'
            on_press: entry.text += ')'
        CustButton:
            text: '√'
            on_press: entry.text += '**(.5)'
        CustButton:
            text: '¹/x'
            on_press: entry.text += '1/'
    RawLayout:
        orientation: 'horizontal'
        CustButton:
            text: 'Del'
            on_press: entry.text = entry.text[:-1]
        CustButton:
            text: 'x²'
            on_press: entry.text += '**2'
        CustButton:
            text: 'xⁿ'
            on_press: entry.text += '**'
        CustButton:
            text: 'π'
            on_press: entry.text += '3.14'

    RawLayout:
        orientation: 'horizontal'
        cols: 4
        CustButton:
            text: 'Clr'
            font_color: [255,0,0,1]
     #       background_normal: ' '
        #    background_color: 1, .3, .4, .85
            on_press: entry.text = ""
        CustButton:
            text: '+'
            on_press: entry.text += self.text
            font_size: 32
        CustButton:
            text: '÷'
            on_press: entry.text += '/'
        CustButton:
            text: '×'
            on_press: entry.text += '*'

    RawLayout:
        rows: 1
        orientation: 'horizontal'
        CustButton:
            text: '7'
            on_press: entry.text += self.text
        CustButton:
            text: '8'
            on_press: entry.text += self.text
        CustButton:
            text: '9'
            on_press: entry.text += self.text
        CustButton:
            text: '-'
            on_press: entry.text += self.text

    RawLayout:
        orientation: 'horizontal'
        rows: 1
        CustButton:
            text: '4'
            on_press: entry.text += self.text
        CustButton:
            text: '5'
            on_press: entry.text += self.text
        CustButton:
            text: '6'
            on_press: entry.text += self.text
        CustButton:
            text: '+'
            on_press: entry.text += self.text

    RawLayout:
        orientation: 'horizontal'
        cols: 3
        CustButton:
            text: '1'
            size_hint: [.5, 1]
            on_press: entry.text += self.text
        CustButton:
            text: '2'
            size_hint: [.5, 1]
            on_press: entry.text += self.text
        CustButton:
            text: '3'
            size_hint: [.5, 1]
            on_press: entry.text += self.text
        CustButton:
            text: ' '
            size_hint: [.5, 1]
            background_normal: ' '
            background_color: 0, 0, 0, 0

    RawLayout:
        orientation: 'horizontal'
        size_hint: [1, .2]
        CustButton:
            text: '0'
            on_press: entry.text += self.text
            size_hint: [.34, 1]
        CustButton:
            text: '.'
            on_press: entry.text += self.text
            size_hint: [.17, 1]
            font_size: 32
        CustButton:
            text: '='
            on_press: calculator.calculate(entry.text)
            size_hint: [.17, 2.4]
    #       background_normal: ' '
        #   background_color:  0, .5, 95, 1

然后查看返回的所有行，其中名为 KEY 的列的值为'PRI'。然后，字段列将为您提供表中构成表主键一部分的列名。

或者：
```
SHOW COLUMNS FROM table_name;
```

如何在数据库级别获取primary_key的列名？

2 个答案: