blocks|key|3471366|text|request变量是更新的行本身。您可以通过request.object.id获取它的对象id，并使用它从数据库获取当前行并检查当前值，如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3471367|Parse.Cloud.beforeSave('votes',+function(request,+response)+{
++++if+(!request.object.isNew())+{
++++var+query+=+new+Parse.Query("votes");
++++query.get(request.object.id,+{+//+Gets+row+you're+trying+to+update
++++++++success:+function(row)+{
++++++++++++if+(row.get('choice')+!==+null)+
++++++++++++++++response.error('Not+allowed+to+change+your+choice+once+submitted');
++++++++++++response.success();+//+Only+after+we+check+for+error+do+we+call+success
++++++++},
++++++++error:+function(row,+error)+{
++++++++++++response.error(error.message);
++++++++}
++++});
}|code-block|syntax|javascript|3471368|entityMap^0|0|7|M|H|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

The <code>request</code> variable is the updated row itself. You can get it's object id through <code>request.object.id</code>and use this to grab the current row from the database and check the current value, like so:

<pre><code>Parse.Cloud.beforeSave('votes', function(request, response) {
 if (!request.object.isNew()) {
 var query = new Parse.Query("votes");
 query.get(request.object.id, { // Gets row you're trying to update
 success: function(row) {
 if (row.get('choice') !== null) 
 response.error('Not allowed to change your choice once submitted');
 response.success(); // Only after we check for error do we call success
 },
 error: function(row, error) {
 response.error(error.message);
 }
 });
}
</code></pre>

blocks|key|4157822|text|虽然Krodmannix的响应是正确的(并且对我很有帮助)，但它有一个完整查询的开销。如果您正在使用beforeSave进行操作，那么您确实希望简化它们。因此，我认为使用fetch命令要好得多。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4157823|Parse.Cloud.beforeSave('votes',+function(request,+response)+{
++++if+(!request.object.isNew())+{
++++++var+Votes+=+Parse.Object.extend("votes");
++++++var+oldVote+=+new+Votes();
++++++oldVote.set("objectId",request.object.id);
++++++oldVote.fetch({
++++++++success:+function(oldVote)+{
++++++++++++if+(oldVote('choice')+!==+null)+{
++++++++++++++++response.error('Not+allowed+to+change+your+choice+once+submitted');
++++++++++++}
++++++++++++else+{
++++++++++++++++response.success();+//+Only+after+we+check+for+error+do+we+call+success
++++++++++++}
++++++++},
++++++++error:+function(oldVote,+error)+{
++++++++++++response.error(error.message);
++++++++}
++++});
});|code-block|syntax|javascript|4157824|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

While Krodmannix's response is correct (and was helpful to me) it has the overhead of a full query. If you are doing things in beforeSave, you really want to streamline them. As a result, I believe a fetch command is much preferable.

<pre><code>Parse.Cloud.beforeSave('votes', function(request, response) {
 if (!request.object.isNew()) {
 var Votes = Parse.Object.extend("votes");
 var oldVote = new Votes();
 oldVote.set("objectId",request.object.id);
 oldVote.fetch({
 success: function(oldVote) {
 if (oldVote('choice') !== null) {
 response.error('Not allowed to change your choice once submitted');
 }
 else {
 response.success(); // Only after we check for error do we call success
 }
 },
 error: function(oldVote, error) {
 response.error(error.message);
 }
 });
});
</code></pre>

blocks|key|4157853|text|您可以使用Parse+DirtyKeys来识别哪个字段已经更改。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4157854|+++Parse.Cloud.beforeSave(Parse.User,+function(request,+response)+{
++for+(dirtyKey+in+request.object.dirtyKeys())+{
++++if+(dirtyKey+===+"yourfieldname")+{
++++++response.error("User+is+not+allowed+to+modify+"+%2B+dirtyKey);
++++++return;
++++}
++}
++response.success();
});|code-block|syntax|javascript|4157855|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can use Parse DirtyKeys to identify which field has changed. 

<pre><code> Parse.Cloud.beforeSave(Parse.User, function(request, response) {
 for (dirtyKey in request.object.dirtyKeys()) {
 if (dirtyKey === "yourfieldname") {
 response.error("User is not allowed to modify " + dirtyKey);
 return;
 }
 }
 response.success();
});
</code></pre>

blocks|key|4157869|text|这样做是有效的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4157870|var+dirtyKeys+=+request.object.dirtyKeys();
var+query+=+new+Parse.Query("Question");
var+clonedData+=+null;
++++++++query.equalTo("objectId",+request.object.id);
++++++++query.find().then(function(data){
++++++++++++var+clonedPatch+=+request.object.toJSON();
++++++++++++clonedData+=+data[0];
++++++++++++clonedData+=+clonedData.toJSON();
++++++++++++console.log("this+is+the+data+:+",+clonedData,+clonedPatch,+dirtyKeys);
++++++++++++response.success();
++++++++}).then(null,+function(err){
++++++++++++console.log("the+error+is+:+",+err);
++++++++});|code-block|syntax|javascript|4157871|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This Worked :

<pre><code>var dirtyKeys = request.object.dirtyKeys();
var query = new Parse.Query("Question");
var clonedData = null;
 query.equalTo("objectId", request.object.id);
 query.find().then(function(data){
 var clonedPatch = request.object.toJSON();
 clonedData = data[0];
 clonedData = clonedData.toJSON();
 console.log("this is the data : ", clonedData, clonedPatch, dirtyKeys);
 response.success();
 }).then(null, function(err){
 console.log("the error is : ", err);
 });
</code></pre>

blocks|key|4157906|text|如果使用的是自托管的Parse+Server，则在请求时有一个称为“原始”的属性，即更改前的对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4157907|Parse.Cloud.beforeSave("Post",+function(request,+response)+{
++++console.log(request.object);++++//contains+changes
++++console.log(request.original);++//contains+original
++++response.success();
});|code-block|syntax|javascript|4157908|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If you are using the self hosted Parse Server, there is a property on request called "original" that is the object before changes.

<pre><code>Parse.Cloud.beforeSave("Post", function(request, response) {
 console.log(request.object); //contains changes
 console.log(request.original); //contains original
 response.success();
});
</code></pre>

In a <code>beforeSave</code> hook I want to obtain the state of the object prior to the update. In this particular case it is to stop a user from changing their choice once they have made it. Pseudo-code looks something like:

<pre><code>If (user has already voted) {
 deny;
} else {
 accept;
}
</code></pre>

And the code that I have so far is:

<pre><code>Parse.Cloud.beforeSave('votes', function(request, response) {
 if (!request.object.isNew()) {
 // This is an update. See if the user already voted
 if (request.object.get('choice') !== null) {
 response.error('Not allowed to change your choice once submitted');
 }
 }
 response.success();
}
</code></pre>

But <code>request.object</code> is the state of the object with the update already applied.

Note that the 'votes' object is created separately so this isn't allowing an insert but not an update will not suffice; I need to know if a given field is already set in the database.

Parse cloudcode beforeSave obtain pre-updated object

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在beforeSave钩子中，我希望在更新之前获得对象的状态。在这种情况下，它是阻止用户改变他们的选择，一旦他们做了。伪代码看起来类似于：If (user has already voted) {  deny;} else {  accept;}到目前为止，我的代码是：Parse.Cloud.beforeSave('v...

问解析cloudcode beforeSave获取预更新的对象
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问解析cloudcode beforeSave获取预更新的对象EN