火力地堡云功能 - 类型错误：当数据存在

Question

无法读取的未定义的属性“数据”我有以下的云功能：

exports.keepPostKeysUpdated = functions.database.ref('/posts/{postid}').onWrite(event => { 
    console.log("write on posts..."); 
    console.log(event.previous.params.postID); 
    console.log(event.data.previous.val()); 
    console.log(event.data.previous.val().postID); 
    var postKey = event.data.previous.val().postID; 


    // When a table, category, or region is changed the old upload has to be deleted 
    if (event.data.previous.exists()) { 
    if (event.data.previous.val().table != event.data.val().table || event.data.previous.val().region != 
     event.data.val().region || event.previous.data.val().category != event.data.val().category) { 
      // category, region, or table was changed 
      console.log(postKey); 
      if (event.data.previous.val().table != event.data.val().table) { 
      console.log("Table was changed"); 
      // delete the post from the old table 
      const oldTable = event.data.previous.val().table; 
      const newTable = event.data.val().table; 

      addToNewTable(newTable, postKey); 
      removePostFromOldTable(oldTable, postKey); 
      } 
      if (event.data.previous.val().category != event.data.val().category) { 
      console.log("Category was changed"); 
      // delete the post from the old category 
      const oldCategory = event.data.previous.val().category; 
      const newCategory = event.data.val().category; 

      addToNewCategory(newCategory, postKey); 
      removePostFromOldCategory(oldCategory, postKey); 
      } 
      if (event.data.previous.val().region != event.data.val().region) { 
      console.log("Region was changed"); 
      // delete post from old region 
      const oldRegion = event.data.previous.val().region; 
      const newRegion = event.data.val().region; 

      addToNewRegion(newRegion, postKey); 
      removePostFromOldRegion(oldRegion, postKey); 
      } 
     } 
     else { 
      return 
     } 
} 
else { 
    // previous value does not exist this case is handled by 
    // copyPostKey 
    return 
} 
}); 

当一个表或区域被改变它的工作完全正常，但无法每次类别被改变。错误来自行var postKey = event.data.previous.val().postID;这个值如何被读取一些而不是其他的？我甚至可以通过控制台登录密钥，但是当我尝试将其分配给postKey时，它表示无法读取密钥。任何想法这个问题是从什么？

的数据总是从我的iOS应用

ref.child("posts").child(editedPost.postID).updateChildValues(["table": editedPost.table]) 
ref.child("posts").child(editedPost.postID).updateChildValues(["category": editedPost.category]) 
ref.child("posts").child(editedPost.postID).updateChildValues(["region": editedPost.region]) 

节点= v6.11.2 火力工具编写同样的方式= 3.10.10

Answer 1

除了马茨回答，您需要调整您的逻辑。

exports.keepPostKeysUpdated = functions.database.ref('/posts/{postid}').onWrite(event => { 
    // When a table, category, or region is changed the old upload has to be deleted 
    if (event.data.previous.exists()) { 
     var postKey = event.data.previous.val().postID; 

如果您在event.data.previous.exists()语句后检查postKey你不应该有任何问题。

它可能值得看看Firebase Documentation，它们有不同的触发器，具体取决于写入操作;

onWrite()，在实时数据库中创建，销毁或更改数据时触发。

onCreate()，在实时数据库中创建新数据时触发。

onUpdate()，在实时数据库中更新数据时触发。

onDelete()，当从实时数据库中删除数据时触发。

在你的情况，你可以改变你的逻辑使用onUpdate

exports.keepPostKeysUpdated = functions.database.ref('/posts/{postid}').onUpdate(event => { 
    var currentValue = currentValue; 
    var previousValue = previousValue; 
    var postKey = previousValue.postID; 


    // When a table, category, or region is changed the old upload has to be deleted 
    if (previousValue.table != currentValue.table || previousValue.region != currentValue.region || event.previous.data.val().category != currentValue.category) { 
     // category, region, or table was changed 
     console.log(postKey); 
     if (previousValue.table != currentValue.table) { 
     console.log("Table was changed"); 
     // delete the post from the old table 
     const oldTable = previousValue.table; 
     const newTable = currentValue.table; 

     addToNewTable(newTable, postKey); 
     removePostFromOldTable(oldTable, postKey); 
     } 
     if (previousValue.category != currentValue.category) { 
     console.log("Category was changed"); 
     // delete the post from the old category 
     const oldCategory = previousValue.category; 
     const newCategory = currentValue.category; 

     addToNewCategory(newCategory, postKey); 
     removePostFromOldCategory(oldCategory, postKey); 
     } 
     if (previousValue.region != currentValue.region) { 
     console.log("Region was changed"); 
     // delete post from old region 
     const oldRegion = previousValue.region; 
     const newRegion = currentValue.region; 

     addToNewRegion(newRegion, postKey); 
     removePostFromOldRegion(oldRegion, postKey); 
     } 
    } else { 
     return 
    } 
}); 

Answer 2

previous.val（）只工作，如果前面的价值存在。如果这是该路径的第一次写入，则可能不存在。您应该检查，看它是否引用它之前就存在：

event.data.previous.exists() 

https://firebase.google.com/docs/database/extend-with-functions#reading_the_previous_value