Azure CosmosDb 存储过程 IfMatch 谓词

Question

在 DocDb 存储过程中，作为检索我正在变异的数据的过程的第一步，我读取并使用数据，前提是它与 etag 匹配，如下所示：

collection.readDocument(reqSelf, function(err, doc) {
    if (doc._etag == requestEtag) {
        // Success - want to update
    } else {
        // CURRENTLY: Discard the read result I just paid lots of RUs to read 
        // IDEALLY: check whether response `options` or similar indicates retrieval
                    was skipped due to doc not being present with that etag anymore 
        ...
        // ... Continue with an alternate strategy
    }
});

有没有办法将 options 传递给 readDocument 调用，以便通知回调 "It's changed so we didn't get it, as you requested"？

（我真正的问题是除了the readDocument undocumentation in the js-server docs我找不到任何文档）

Answer 1

感谢@Nick Chapsas 的一些推动，this self-answer from @Redman 我发现在我的情况下我可以实现我的目标（通过 self-link 阅读当前文档，或者通过在存储过程中生成一个 Alt link 来替换它的更新版本具有相同的 id)，如下所示：

var docId = collection.getAltLink() + "/docs/"+req.id;
var isAccepted = collection.readDocument(docId, {}, function (err, doc, options) {
    if (err) throw err;
    // Will be null or not depending on whether it exists
    executeUpsert(doc);
});
if (!isAccepted) throw new Error("readDocument not Accepted");

Answer 2

从技术上讲，您可以通过创建一个 responseOptions 对象并将其传递给调用来实现。

function sample(selfLink, requestEtag) {
    var collection = getContext().getCollection();

    var responseOptions = { accessCondition: { type: "IfMatch", condition: requestEtag } };

    var isAccepted = collection.readDocument(selfLink, responseOptions, function(err, doc, options) {
        if(err){
            throw new Error('Error thrown. Check the status code for PreconditionFailed errors');
        }

        var response = getContext().getResponse();
        response.setBody(doc);

    });

    if (!isAccepted) throw new Error('The query was not accepted by the server.');
}

但是，即使您提供的 etag 不是文档所具有的 etag，您也不会收到错误消息，并且会正确取回文档本身。只是不应该在存储过程中使用 readDocument 函数。

Azure CosmosDb 存储过程 IfMatch 谓词

Azure CosmosDb Stored Procedure IfMatch Predicate

javascript

azure

stored-procedures

azure-cosmosdb

etag