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我在 AppSync GraphQL 查询的帮助下开发 DynamoDB。

我有一个 DynamoDB 表，其中用户名是分区键（散列键），timestamp_value 是排序键（范围键）。

我针对一项保存两件事，即一项是阅读，第二项是活动（如锻炼、运动等）。为了添加这两项，我们有不同的 UI 屏幕。这两件事可能具有相同的时间戳，因此它将保存在一个项目中。

所以现在我需要一个可用于上述操作的 upsert（插入或更新）查询，因为当您尝试插入新读数时，它将检查该项目是否存在。如果存在，那么它将更新或不更新，然后它将插入项目，并且当用户想要添加新活动时必须发生同样的事情。

我对文档感到困惑，并且没有找到用于执行 upsert 操作的确切 AppSync 请求映射解析器。

下面是 PutItem 请求映射解析器：-

    {
      "version": "2017-02-28",
      "operation": "PutItem",
      "key": {
         "username": $util.dynamodb.toDynamoDBJson($ctx.identity.username),
         "timestamp": $util.dynamodb.toDynamoDBJson($ctx.args.input.timestamp),
      },
      "attributeValues": $util.dynamodb.toMapValuesJson($ctx.args.input),
      "condition": {
         "expression": "attribute_not_exists(#timestamp)",
         "expressionNames": {
           "#timestamp": "timestamp",
         },
      },
   }

以下是 UpdateItem 请求映射解析器：-

{
  "version": "2017-02-28",
  "operation": "UpdateItem",
  "key": {
    "username": $util.dynamodb.toDynamoDBJson($ctx.identity.username),
    "timestamp": $util.dynamodb.toDynamoDBJson($ctx.args.input.timestamp),
  },

  ## Set up some space to keep track of things we're updating **
  #set( $expNames  = {} )
  #set( $expValues = {} )
  #set( $expSet = {} )
  #set( $expAdd = {} )
  #set( $expRemove = [] )

  ## Iterate through each argument, skipping keys **
  #foreach( $entry in $util.map.copyAndRemoveAllKeys($ctx.args.input, ["username", "timestamp"]).entrySet() )
    #if( $util.isNull($entry.value) )
      ## If the argument is set to "null", then remove that attribute from the item in DynamoDB **

      #set( $discard = ${expRemove.add("#${entry.key}")} )
      $!{expNames.put("#${entry.key}", "${entry.key}")}
    #else
      ## Otherwise set (or update) the attribute on the item in DynamoDB **

      $!{expSet.put("#${entry.key}", ":${entry.key}")}
      $!{expNames.put("#${entry.key}", "${entry.key}")}
      $!{expValues.put(":${entry.key}", $util.dynamodb.toDynamoDB($entry.value))}
    #end
  #end

  ## Start building the update expression, starting with attributes we're going to SET **
  #set( $expression = "" )
  #if( !${expSet.isEmpty()} )
    #set( $expression = "SET" )
    #foreach( $entry in $expSet.entrySet() )
      #set( $expression = "${expression} ${entry.key} = ${entry.value}" )
      #if ( $foreach.hasNext )
        #set( $expression = "${expression}," )
      #end
    #end
  #end

  ## Continue building the update expression, adding attributes we're going to ADD **
  #if( !${expAdd.isEmpty()} )
    #set( $expression = "${expression} ADD" )
    #foreach( $entry in $expAdd.entrySet() )
      #set( $expression = "${expression} ${entry.key} ${entry.value}" )
      #if ( $foreach.hasNext )
        #set( $expression = "${expression}," )
      #end
    #end
  #end

  ## Continue building the update expression, adding attributes we're going to REMOVE **
  #if( !${expRemove.isEmpty()} )
    #set( $expression = "${expression} REMOVE" )

    #foreach( $entry in $expRemove )
      #set( $expression = "${expression} ${entry}" )
      #if ( $foreach.hasNext )
        #set( $expression = "${expression}," )
      #end
    #end
  #end

  ## Finally, write the update expression into the document, along with any expressionNames and expressionValues **
  "update": {
    "expression": "${expression}",
    #if( !${expNames.isEmpty()} )
      "expressionNames": $utils.toJson($expNames),
    #end
    #if( !${expValues.isEmpty()} )
      "expressionValues": $utils.toJson($expValues),
    #end
  },

  "condition": {
    "expression": "SET attribute_exists(#username) AND attribute_not_exists(#timestamp)",
    "expressionNames": {
      "#username": "username",
      "#timestamp": "timestamp",
    },
  }
}

那么如何更新解析器以便进行 upsert 操作呢？

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0 回答 0