使用AWS AppSync中的列表查询DynamoDB

问题描述

我正在尝试使用IN使用列表构建AWS AppSync查询:

I am trying to build an AWS AppSync query with a list using IN:

{
    "version" : "2017-02-28",
    "operation" : "Query",
    "index" : "my-index",
    "query" : {
        "expression": "id IN :ids",
        "expressionValues" : { ":ids" : $util.dynamodb.toStringSet($ctx.args.ids) }
    },
    "limit": $util.defaultIfNull(${ctx.args.first}, 20),
    "nextToken": $util.toJson($util.defaultIfNullOrBlank($ctx.args.after, null))
}

但是，请使用以下参数进行尝试:

However, trying it out with parameters like:

query ListItemsWithIdList {
  listItemsWithIdList(first:20, ids: ["id1", "id2"]) {
    items {
      id
    }
    nextToken
  }
}

它抛出一个错误:

Unable to parse the JSON document: 'Unexpected character ('S' (code 83)): was expecting double-quote to start field name
at [Source: (String)\"{
    \"version\" : \"2017-02-28\",
    \"operation\" : \"Query\",
    \"index\" : \"my-index\",
    \"query\" : {
        \"expression\": \"id IN :ids\",
        \"expressionValues\" : { \":ids\" : {SS=[id1, id2]} }
    },
    \"limit\": 20,
    \"nextToken\": null
}\"; line: 7, column: 47]'"

使用IN进行查询比较运算符似乎可以；但是，如何传递String List作为参数，并获取ID在提供的那些参数之中的结果?

It seems OK to use IN for query comparison operator; however, how can I pass a String List as a parameter and fetch the results whose IDs are among those parameters supplied?

编辑:更正了变量名的错字.

Corrected variable name typo.

推荐答案

我不认为AWS AppSync仅暂时支持IN.我尝试测试您的方案并使用contains()函数提供解决方案.

I don't think AWS AppSync support IN just for now. I try to test your scenario and come up with a solution using contains() function.

以下是查询后的结果:

另一种替代解决方案是使用Scan(不推荐)

Another alternative solution is to use Scan (not recommended)

{
    "version" : "2017-02-28",
    "operation" : "Scan",
    "filter" : {
        "expression": "contains (:authors, author)",
        "expressionValues" : {
            ":authors" : $util.dynamodb.toDynamoDBJson($ctx.args.authors)
        }
    }
}

顺便说一句，AWS AppSync支持BatchGetItem操作.您可以在单个查询中传递键列表，然后从表中返回结果.
参考: https://docs.aws.amazon.com/appsync/latest/devguide/tutorial-dynamodb-batch.html
这是一个示例，我测试了它是否像魅力一样工作:

Btw, AWS AppSync support BatchGetItem operation. You can pass a list of keys in a single query and return the results from a table.
Reference: https://docs.aws.amazon.com/appsync/latest/devguide/tutorial-dynamodb-batch.html
Here is an example and I tested it worked like charm:

## REQUEST MAPPING
#set($authors = [])
#foreach( $author in $ctx.args.authors )
    #set($map = {})
    $util.qr($map.put("author", $util.dynamodb.toString($author)))
    $util.qr($authors.add($map))
#end

{
    "version" : "2018-05-29",
    "operation" : "BatchGetItem",
    "tables" : {
        "tbDiary": {
            "keys": $util.toJson($authors),
            "consistentRead": true
        }
    }
}

## RESPONSE MAPPING
$util.toJson($ctx.result.data.tbDiary)

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