Azure Cosmos DB Patch操作：节点不存在时如何创建节点结构？

问题场景 #

我尝试执行以下Patch操作更新Cosmos DB文档：

ItemResponse<dynamic> response = await _container.PatchItemAsync<dynamic>(
    id: loanParent.LoanNumber,
    partitionKey: new PartitionKey(loanParent.LoanNumber),
    patchOperations: new[] {
        PatchOperation.Replace("/loandetails/loanname", loanParent.Loan.LoanDetails.LoanName),
        PatchOperation.Replace("/loandetails/loandescription", loanParent.Loan.LoanDetails.LoanDescription)
    }
);

当前目标文档结构如下：

{
    "loannumber": "abc123",
    "id": "abc123",
    "participants": [
        {
            "firstname": "alex",
            "lastname": "gordon"
        },
        {
            "firstname": "liza",
            "lastname": "gordon"
        }
    ],
    "_rid": "1sAyAggggggA==",
    "_self": "dbs/1sAyAA=gggggAAAAAAAA==/",
    "_etag": "\"d900c069-0000-4440-0000-63642d840000\"",
    "_attachments": "attachments/",
    "_ts": 1ddd636
}

执行后触发异常：

Microsoft.Azure.Cosmos.CosmosException : Response status code does not indicate success: BadRequest (400); Substatus: 0; ActivityId: a6ab67d6-f73e-4b3c-b03e-1d9b6cc54dba; Reason: (Message: {"Errors":["For Operation(1): Given Operation can only create a child object of an existing node(array or object) and cannot create path recursively, no path found beyond: 'loandetails'. Learn more: https://aka.ms/cosmosdbpatchdocs"]}

请问如何创建不存在的节点结构？

解决方案 #

Cosmos DB的Patch操作不会自动递归创建父节点，必须先确保上层节点存在，再操作子属性。推荐两种实现方式：

方式一：先创建父节点，再更新子属性 #

先用PatchOperation.Add创建/loandetails空对象，再执行Replace操作更新子属性：

ItemResponse<dynamic> response = await _container.PatchItemAsync<dynamic>(
    id: loanParent.LoanNumber,
    partitionKey: new PartitionKey(loanParent.LoanNumber),
    patchOperations: new[] {
        // 先创建loandetails空对象
        PatchOperation.Add("/loandetails", new {}),
        // 再替换子属性
        PatchOperation.Replace("/loandetails/loanname", loanParent.Loan.LoanDetails.LoanName),
        PatchOperation.Replace("/loandetails/loandescription", loanParent.Loan.LoanDetails.LoanDescription)
    }
);

方式二：一次性创建完整嵌套结构 #

直接用PatchOperation.Add添加包含所有子属性的loandetails对象，一步完成结构创建和赋值：

ItemResponse<dynamic> response = await _container.PatchItemAsync<dynamic>(
    id: loanParent.LoanNumber,
    partitionKey: new PartitionKey(loanParent.LoanNumber),
    patchOperations: new[] {
        PatchOperation.Add("/loandetails", new {
            loanname = loanParent.Loan.LoanDetails.LoanName,
            loandescription = loanParent.Loan.LoanDetails.LoanDescription
        })
    }
);

注意事项 #

如果loandetails节点可能已存在，建议先通过条件Patch判断节点是否存在，避免覆盖原有数据；或者使用PatchOperation.Upsert（部分SDK版本支持）来实现存在则更新、不存在则创建的逻辑。

内容的提问来源于stack exchange，提问作者Alex Gordon