（对不起，这个问题比我想象的要久...）
我将Go和MongoDB与mgo驱动程序配合使用。我试图在同一个MongoDB集合中坚持并检索不同的结构（实现一个通用接口）。我来自Java世界（使用Spring可以很容易地完成它，而实际上没有配置），并且我很难用Go来做类似的事情。 我已经阅读了我能找到的所有上一篇相关文章或帖子或StackExchange问题，但仍然没有找到完整的解决方案。这包括：
这是我用于测试的简化设置。假设两个结构S1和S2实现了公共接口I。 S2具有类型为S1的隐式字段，这意味着结构化的S2嵌入了一个S1值，而类型化的S2实现了{{1 }}。
I现在，我可以使用type I interface {
f1()
}
type S1 struct {
X int
}
type S2 struct {
S1
Y int
}
func (*S1) f1() {
fmt.Println("f1")
}
轻松保存S1或S2的实例，但是例如，要使用mgo.Collection.Insert()正确填充值，我需要传递一个指针到mgo.Collection.Find().One()或S1的现有值，这意味着我已经知道我要读取的对象的类型！
我希望能够从MongoDB集合中检索文档，而无需知道它是S2还是S1，或者实际上是任何实现S2的对象。
到目前为止，这就是我要去的地方：我没有保存直接保存要保留的对象，而是保存了一个I结构，该结构包含MongoDB id，类型的标识符和实际值。类型标识符是 packageName +“的串联。 + typeName ，它用于在类型注册表中查找类型，因为在Go中没有从类型名映射到Type对象的本地机制。这意味着我需要注册我希望能够持久和检索的类型，但是我可以接受。这是怎么回事：
Wrapper这是类型注册表的代码：
typeregistry.Register(reflect.TypeOf((*S1)(nil)).Elem())
typeregistry.Register(reflect.TypeOf((*S2)(nil)).Elem())
用于保存对象的代码非常简单：
var types map[string]reflect.Type
func init() {
types = make(map[string]reflect.Type)
}
func Register(t reflect.Type) {
key := GetKey(t)
types[key] = t
}
func GetKey(t reflect.Type) string {
key := t.PkgPath() + "." + t.Name()
return key
}
func GetType(key string) reflect.Type {
t := types[key]
return t
}
用于检索对象的代码比较棘手：
func save(coll *mgo.Collection, s I) (bson.ObjectId, error) {
t := reflect.TypeOf(s)
wrapper := Wrapper{
Id: bson.NewObjectId(),
TypeKey: typeregistry.GetKey(t),
Val: s,
}
return wrapper.Id, coll.Insert(wrapper)
}
这部分工作是因为正确键入了返回的对象，但是我不知道是如何用从MongoDB检索到的数据填充值func getById(coll *mgo.Collection, id interface{}) (*I, error) {
// read wrapper
wrapper := Wrapper{}
err := coll.Find(bson.M{"_id": id}).One(&wrapper)
if err != nil {
return nil, err
}
// obtain Type from registry
t := typeregistry.GetType(wrapper.TypeKey)
// get a pointer to a new value of this type
pt := reflect.New(t)
// FIXME populate value using wrapper.Val (type bson.M)
// HOW ???
// return the value as *I
i := pt.Elem().Interface().(I)
return &i, nil
}
的，该数据存储为pt wrapper.Val。
我尝试了以下操作，但不起作用：
bson.M所以基本上剩下的问题是：如何从m := wrapper.Val.(bson.M)
bsonBytes, _ := bson.Marshal(m)
bson.Unmarshal(bsonBytes, pt)
值填充未知结构？我敢肯定必须有一个简单的解决方案...
预先感谢您的帮助。
这里是Github要点，其中包含所有代码：https://gist.github.com/ogerardin/5aa272f69563475ba9d7b3194b12ae57
答案 0 :(得分：1)
首先，您应该始终检查返回的错误。 bson.Marshal()和bson.Unmarshal()返回您未检查的错误。这样做揭示了为什么它不起作用：
unmarshal无法处理结构值。使用指针
import javax.swing.border.LineBorder
import java.util.ArrayList
import javax.swing.event.DocumentListener
import java.awt.*
import java.awt.event.*
import javax.swing.*
import javax.swing.event.DocumentEvent
/**
* Author of the original version: David @ https://stackoverflow.com/users/1133011/david-kroukamp
*/
class Test {
init {
val frame = JFrame()
frame.defaultCloseOperation = JFrame.EXIT_ON_CLOSE
val f = JTextField(10)
val autoSuggestor = object : AutoSuggestor(f, frame, ArrayList(), Color.WHITE.brighter(), Color.BLUE, Color.RED, 0.75f) {
override fun wordTyped(typedWord: String?): Boolean {
//create list for dictionary this in your case might be done via calling a method which queries db and returns results as arraylist
val words = ArrayList<String>()
words.add("hello")
words.add("heritage")
words.add("happiness")
words.add("goodbye")
words.add("cruel")
words.add("car")
words.add("war")
words.add("will")
words.add("world")
words.add("wall")
setDictionary(words)
//addToDictionary("bye");//adds a single word
return super.wordTyped(typedWord)//now call super to check for any matches against newest dictionary
}
}
val p = JPanel()
p.add(f)
frame.add(p)
frame.pack()
frame.isVisible = true
}
companion object {
@JvmStatic
fun main(args: Array<String>) {
SwingUtilities.invokeLater { Test() }
}
}
}
internal open class AutoSuggestor(val textField: JTextField, val container: Window, words: ArrayList<String>, popUpBackground: Color, private val suggestionsTextColor: Color, private val suggestionFocusedColor: Color, opacity: Float, private val callback: (String) -> Unit = {}) {
private val suggestionsPanel: JPanel
val autoSuggestionPopUpWindow: JWindow
private var typedWord: String? = null
private val dictionary = ArrayList<String>()
private var currentIndexOfSpace: Int = 0
private var tW: Int = 0
private var tH: Int = 0
private val documentListener = object : DocumentListener {
override fun insertUpdate(de: DocumentEvent) {
checkForAndShowSuggestions()
}
override fun removeUpdate(de: DocumentEvent) {
checkForAndShowSuggestions()
}
override fun changedUpdate(de: DocumentEvent) {
checkForAndShowSuggestions()
}
}
val addedSuggestionLabels: ArrayList<SuggestionLabel>
get() {
val sls = ArrayList<SuggestionLabel>()
for (i in 0 until suggestionsPanel.componentCount) {
if (suggestionsPanel.getComponent(i) is SuggestionLabel) {
val sl = suggestionsPanel.getComponent(i) as SuggestionLabel
sls.add(sl)
}
}
return sls
}
//get newest word after last white space if any or the first word if no white spaces
val currentlyTypedWord: String
get() {
val text = textField.text
var wordBeingTyped = ""
if (text.contains(" ")) {
val tmp = text.lastIndexOf(" ")
if (tmp >= currentIndexOfSpace) {
currentIndexOfSpace = tmp
wordBeingTyped = text.substring(text.lastIndexOf(" "))
}
} else {
wordBeingTyped = text
}
return wordBeingTyped.trim { it <= ' ' }
}
init {
this.textField.document.addDocumentListener(documentListener)
setDictionary(words)
typedWord = ""
currentIndexOfSpace = 0
tW = 0
tH = 0
autoSuggestionPopUpWindow = JWindow(container)
autoSuggestionPopUpWindow.opacity = opacity
suggestionsPanel = JPanel()
suggestionsPanel.layout = GridLayout(0, 1)
suggestionsPanel.background = popUpBackground
addFocusListenersToHandleVisibilityOfPopUpWindow()
addKeyBindingToRequestFocusInPopUpWindow()
}
private fun addFocusListenersToHandleVisibilityOfPopUpWindow() {
textField.addFocusListener(object:FocusListener {
override fun focusLost(e: FocusEvent?) {
var focusOnPopUp = false
for (i in 0 until suggestionsPanel.componentCount) {
if (suggestionsPanel.getComponent(i) is SuggestionLabel) {
val label = suggestionsPanel.getComponent(i) as SuggestionLabel
if (label.isFocused)
focusOnPopUp = true
}
}
if (!focusOnPopUp && !shouldShowPopUpWindow) {
autoSuggestionPopUpWindow.isVisible = false
}
}
override fun focusGained(e: FocusEvent?) {
shouldShowPopUpWindow = false
}
})
}
private fun addKeyBindingToRequestFocusInPopUpWindow() {
textField.getInputMap(JComponent.WHEN_FOCUSED).put(KeyStroke.getKeyStroke(KeyEvent.VK_ESCAPE, 0, true), "Escape released")
textField.actionMap.put("Escape released", object : AbstractAction() {
override fun actionPerformed(ae: ActionEvent) {// Hide the popwindow
shouldShowPopUpWindow = false
autoSuggestionPopUpWindow.isVisible = false
}
})
textField.getInputMap(JComponent.WHEN_FOCUSED).put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, true), "Down released")
textField.actionMap.put("Down released", object : AbstractAction() {
override fun actionPerformed(ae: ActionEvent) {//focuses the first label on popwindow
for (i in 0 until suggestionsPanel.componentCount) {
if (suggestionsPanel.getComponent(i) is SuggestionLabel) {
(suggestionsPanel.getComponent(i) as SuggestionLabel).isFocused = true
autoSuggestionPopUpWindow.toFront()
autoSuggestionPopUpWindow.requestFocusInWindow()
suggestionsPanel.requestFocusInWindow()
suggestionsPanel.getComponent(i).requestFocusInWindow()
break
}
}
}
})
textField.getInputMap(JComponent.WHEN_FOCUSED).put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, true), "Up released")
textField.actionMap.put("Up released", object : AbstractAction() {
override fun actionPerformed(ae: ActionEvent) {//focuses the last label on popwindow
for (i in 0 until suggestionsPanel.componentCount) {
val reverseIndex = suggestionsPanel.componentCount-1 - i
if (suggestionsPanel.getComponent(reverseIndex) is SuggestionLabel) {
(suggestionsPanel.getComponent(reverseIndex) as SuggestionLabel).isFocused = true
autoSuggestionPopUpWindow.toFront()
autoSuggestionPopUpWindow.requestFocusInWindow()
suggestionsPanel.requestFocusInWindow()
suggestionsPanel.getComponent(reverseIndex).requestFocusInWindow()
break
}
}
}
})
suggestionsPanel.getInputMap(JComponent.WHEN_FOCUSED).put(KeyStroke.getKeyStroke(KeyEvent.VK_ESCAPE, 0, true), "Escape released")
suggestionsPanel.actionMap.put("Escape released", object : AbstractAction() {
override fun actionPerformed(ae: ActionEvent) {// Hide the popwindow
shouldShowPopUpWindow = false
autoSuggestionPopUpWindow.isVisible = false
}
})
suggestionsPanel.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT).put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, true), "Up released")
suggestionsPanel.actionMap.put("Up released", object : AbstractAction() {
override fun actionPerformed(ae: ActionEvent) {//allows scrolling of labels in pop window (I know very hacky for now :))
val sls = addedSuggestionLabels
val max = sls.size
var indexOfFocusedSuggestion = -1
for (i in 0 until max) {
val sl = sls[i]
if ( sl.isFocused )
indexOfFocusedSuggestion = i
}
if (indexOfFocusedSuggestion - 1 < 0) {
sls[indexOfFocusedSuggestion].isFocused = false
autoSuggestionPopUpWindow.isVisible = false
setFocusToTextField()
checkForAndShowSuggestions()//fire method as if document listener change occured and fired it
}
else {
sls[indexOfFocusedSuggestion].isFocused = false
sls[indexOfFocusedSuggestion-1].isFocused = true
autoSuggestionPopUpWindow.toFront()
autoSuggestionPopUpWindow.requestFocusInWindow()
suggestionsPanel.requestFocusInWindow()
suggestionsPanel.getComponent(indexOfFocusedSuggestion-1).requestFocusInWindow()
}
}
})
suggestionsPanel.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT).put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, true), "Down released")
suggestionsPanel.actionMap.put("Down released", object : AbstractAction() {
override fun actionPerformed(ae: ActionEvent) {//allows scrolling of labels in pop window (I know very hacky for now :))
val sls = addedSuggestionLabels
val max = sls.size
var indexOfFocusedSuggestion = -1
for (i in 0 until max) {
val sl = sls[i]
if ( sl.isFocused )
indexOfFocusedSuggestion = i
}
if (indexOfFocusedSuggestion + 1 >= max) {
sls[indexOfFocusedSuggestion].isFocused = false
autoSuggestionPopUpWindow.isVisible = false
setFocusToTextField()
checkForAndShowSuggestions()//fire method as if document listener change occured and fired it
}
else {
sls[indexOfFocusedSuggestion].isFocused = false
sls[indexOfFocusedSuggestion+1].isFocused = true
autoSuggestionPopUpWindow.toFront()
autoSuggestionPopUpWindow.requestFocusInWindow()
suggestionsPanel.requestFocusInWindow()
suggestionsPanel.getComponent(indexOfFocusedSuggestion+1).requestFocusInWindow()
}
}
})
}
private fun setFocusToTextField() {
container.toFront()
container.requestFocusInWindow()
textField.requestFocusInWindow()
}
var shouldShowPopUpWindow = false
private fun checkForAndShowSuggestions() {
typedWord = currentlyTypedWord
suggestionsPanel.removeAll()//remove previos words/jlabels that were added
//used to calcualte size of JWindow as new Jlabels are added
tW = 0
tH = 0
val added = wordTyped(typedWord)
if (!added) {
if (autoSuggestionPopUpWindow.isVisible) {
autoSuggestionPopUpWindow.isVisible = false
}
} else {
shouldShowPopUpWindow = true
showPopUpWindow()
setFocusToTextField()
}
}
protected fun addWordToSuggestions(word: String) {
val suggestionLabel = SuggestionLabel(word, suggestionFocusedColor, suggestionsTextColor, this, callback)
calculatePopUpWindowSize(suggestionLabel)
suggestionsPanel.add(suggestionLabel)
}
private fun calculatePopUpWindowSize(label: JLabel) {
//so we can size the JWindow correctly
if (tW < label.preferredSize.width) {
tW = label.preferredSize.width
}
tH += label.preferredSize.height
}
private fun showPopUpWindow() {
autoSuggestionPopUpWindow.contentPane.add(suggestionsPanel)
autoSuggestionPopUpWindow.minimumSize = Dimension(textField.width, 30)
autoSuggestionPopUpWindow.setSize(tW, tH)
autoSuggestionPopUpWindow.isVisible = true
var windowX = 0
var windowY = 0
windowX = container.getX() + textField.x + 5
if (suggestionsPanel.height > autoSuggestionPopUpWindow.minimumSize.height) {
windowY = container.getY() + textField.y + textField.height + autoSuggestionPopUpWindow.minimumSize.height
} else {
windowY = container.getY() + textField.y + textField.height + autoSuggestionPopUpWindow.height
}
autoSuggestionPopUpWindow.setLocation(windowX, windowY)
autoSuggestionPopUpWindow.minimumSize = Dimension(textField.width, 30)
autoSuggestionPopUpWindow.revalidate()
autoSuggestionPopUpWindow.repaint()
}
fun setDictionary(words: ArrayList<String>?) {
dictionary.clear()
if (words == null) {
return //so we can call constructor with null value for dictionary without exception thrown
}
for (word in words) {
dictionary.add(word)
}
}
fun addToDictionary(word: String) {
dictionary.add(word)
}
open fun wordTyped(typedWord: String?): Boolean {
if (typedWord!!.isEmpty()) {
return false
}
var suggestionAdded = false
for (word in dictionary) {//get words in the dictionary which we added
var fullyMatches = word.length >= typedWord.length
for (i in 0 until typedWord.length) {//each string in the word
if (word.length > i && !typedWord.toLowerCase().startsWith(word.toLowerCase()[i].toString(), i)) {//check for match
fullyMatches = false
break
}
}
if (fullyMatches) {
addWordToSuggestions(word)
suggestionAdded = true
}
}
return suggestionAdded
}
}
internal class SuggestionLabel(string: String, private val suggestionBorderColor: Color, private val suggestionsTextColor: Color, private val autoSuggestor: AutoSuggestor, private val callback: (String) -> Unit) : JLabel(string) {
var isFocused = false
set(focused) {
if (focused) {
border = LineBorder(suggestionBorderColor)
} else {
border = null
}
repaint()
field = focused
}
private val autoSuggestionsPopUpWindow: JWindow
private val textField: JTextField
init {
this.textField = autoSuggestor.textField
this.autoSuggestionsPopUpWindow = autoSuggestor.autoSuggestionPopUpWindow
initComponent()
}
private fun initComponent() {
isFocusable = true
foreground = suggestionsTextColor
addMouseListener(object : MouseAdapter() {
override fun mouseClicked(me: MouseEvent) {
super.mouseClicked(me)
replaceWithSuggestedText()
autoSuggestionsPopUpWindow.isVisible = false
}
})
getInputMap(JComponent.WHEN_FOCUSED).put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER, 0, true), "Enter released")
actionMap.put("Enter released", object : AbstractAction() {
override fun actionPerformed(ae: ActionEvent) {
replaceWithSuggestedText()
autoSuggestionsPopUpWindow.isVisible = false
}
})
getInputMap(JComponent.WHEN_FOCUSED).put(KeyStroke.getKeyStroke(KeyEvent.VK_ESCAPE, 0, true), "Escape released")
actionMap.put("Escape released", object : AbstractAction() {
override fun actionPerformed(ae: ActionEvent) {// Hide the popwindow
autoSuggestionsPopUpWindow.isVisible = false
}
})
}
private fun replaceWithSuggestedText() {
val suggestedWord = text
val text = textField.text
val typedWord = autoSuggestor.currentlyTypedWord
val t = text.substring(0, text.lastIndexOf(typedWord))
val tmp = t + text.substring(text.lastIndexOf(typedWord)).replace(typedWord, suggestedWord)
textField.text = tmp
callback(tmp)
}
}
的类型为reflect.Value（恰好是一个结构），而不是您应该传递给pt的东西。您应该通过例如指向要解组的结构值的指针（它将包装在bson.Unmarshal()值中）。因此，请对Value.Interface()返回的值调用reflect.New()：
interface{}您可以将其传递给pt := reflect.New(t).Interface()
：
bson.Unmarshal()（在您的真实代码中，您除了恐慌之外还想做其他事情，这只是表明您应该始终检查错误！）
还请注意，可以将地图直接转换为结构（直接意味着无需封送处理和拆封处理）。您可以手工实现它，也可以使用现成的第三方库。有关详细信息，请参见Converting map to struct
还请注意，还有更多聪明的方法可以解决您想做的事情。您可以将类型存储在ID本身中，因此，如果您具有ID，则可以构造类型的值以将其解组到查询结果中，因此可以跳过此整个过程。这样会更简单，更有效。
例如，您可以使用以下ID结构：
bsonBytes, err := bson.Marshal(m)
if err != nil {
panic(err)
}
if err = bson.Unmarshal(bsonBytes, pt); err != nil {
panic(err)
}
例如：
<type>-<id>
在获取/加载该文档时，可以使用反射创建一个my.package.S1-123
值，然后直接将其解编（将其传递给my.package.S1）。
答案 1 :(得分：0)
根据@icza的评论，这是getById()的修改后的版本，实际上可以工作：
func getById(coll *mgo.Collection, id interface{}) (*I, error) {
// read wrapper
wrapper := Wrapper{}
err := coll.Find(bson.M{"_id": id}).One(&wrapper)
if err != nil {
return nil, err
}
// obtain Type from registry
t := typeregistry.GetType(wrapper.TypeKey)
// get a pointer to a new value of this type
pt := reflect.New(t)
// populate value using wrapper.Val
err = mapstructure.Decode(wrapper.V, pt.Interface())
if err != nil {
return nil, err
}
// return the value as *I
i := pt.Elem().Interface().(I)
return &i, nil
}
从bson.M到结构的转换由https://github.com/mitchellh/mapstructure处理，而不是编组/拆组。