如何定义AppSync Schema与Resolver，使GraphQL扫描DynamoDB返回键值对config_value？

Got it! Let's break down exactly how to set up your AppSync Schema and Resolvers to return the config_value as key-value pairs from your DynamoDB collection. I'll cover two common scenarios: returning the nested object directly as JSON, and converting it into a list of structured key-value pairs if that's what you prefer.

Step 1: Define the AppSync GraphQL Schema #

First, we need to define types that match your data structure. Here are two options based on how you want the config_value returned:

Option 1: Return config_value as a JSON Object #

This keeps the original nested structure intact and is the simplest approach:

# Define the main Config type matching your DynamoDB item
type Config {
  config_name: String!
  config_value: JSON! # AppSync's built-in JSON scalar handles nested objects
}

# Define your Query operations
type Query {
  # Fetch a single config by name (e.g., COLOR_PALETTE)
  getConfig(configName: String!): Config
  # Scan all configs in the DynamoDB table
  listAllConfigs: [Config]
}

# Ensure the JSON scalar is available (AppSync includes this by default)
scalar JSON

Option 2: Return config_value as a List of Key-Value Pairs #

If you want explicitly structured key-value entries instead of a raw JSON object, define a KeyValue type:

type KeyValue {
  key: String!
  value: String!
}

type Config {
  config_name: String!
  config_value: [KeyValue]! # Array of key-value pairs
}

type Query {
  getConfig(configName: String!): Config
  listAllConfigs: [Config]
}

Step 2: Configure DynamoDB Resolvers #

Now let's set up the VTL (Velocity Template Language) resolvers for each query. I'll assume your DynamoDB table uses config_name as the primary key, and config_value is stored as a stringified JSON (a common practice). If it's stored as a DynamoDB Map (M type), I'll note the adjustment needed.

Resolver for getConfig (Single Item Query) #

Request Template

This template fetches a single item by config_name:

{
  "version": "2017-02-28",
  "operation": "GetItem",
  "key": {
    "config_name": { "S": "${ctx.args.configName}" }
  }
}

Response Template (Option 1: JSON Object)

Parse the stringified config_value into a JSON object and return it:

# If config_value is stored as a stringified JSON (S type)
$util.toJson({
  "config_name": $ctx.result.config_name.S,
  "config_value": $util.parseJson($ctx.result.config_value.S)
})

# If config_value is stored as a DynamoDB Map (M type), use this instead:
# $util.toJson({
#   "config_name": $ctx.result.config_name.S,
#   "config_value": $util.dynamodb.toJsonObject($ctx.result.config_value)
# })

Response Template (Option 2: Key-Value List)

Convert the nested object into an array of KeyValue entries:

# Parse the stored config_value into a JSON object
#set($configValueObj = $util.parseJson($ctx.result.config_value.S))
#set($keyValuePairs = [])

# Loop through each key-value entry in the object
#foreach($entry in $configValueObj.entrySet())
  #set($kv = {
    "key": $entry.key,
    "value": $entry.value
  })
  #set($discard = $keyValuePairs.add($kv))
#end

# Format and return the final result
$util.toJson({
  "config_name": $ctx.result.config_name.S,
  "config_value": $keyValuePairs
})

Resolver for listAllConfigs (Scan Operation) #

Request Template

This template scans the entire DynamoDB table:

{
  "version": "2017-02-28",
  "operation": "Scan"
}

Response Template (Option 1: JSON Object)

Map over all scanned items and parse each config_value:

# If config_value is stored as stringified JSON
$util.toJson($ctx.result.items.map(item => ({
  config_name: item.config_name.S,
  config_value: $util.parseJson(item.config_value.S)
})))

# If config_value is a DynamoDB Map, use:
# $util.toJson($ctx.result.items.map(item => ({
#   config_name: item.config_name.S,
#   config_value: $util.dynamodb.toJsonObject(item.config_value)
# })))

Response Template (Option 2: Key-Value List)

Process each item to convert config_value into key-value pairs:

#set($finalResults = [])

#foreach($item in $ctx.result.items)
  #set($configValueObj = $util.parseJson($item.config_value.S))
  #set($keyValuePairs = [])
  
  #foreach($entry in $configValueObj.entrySet())
    #set($kv = {
      "key": $entry.key,
      "value": $entry.value
    })
    #set($discard = $keyValuePairs.add($kv))
  #end
  
  #set($configItem = {
    "config_name": $item.config_name.S,
    "config_value": $keyValuePairs
  })
  #set($discard = $finalResults.add($configItem))
#end

$util.toJson($finalResults)

Quick Notes #

• Storage Type Check: Double-check how config_value is stored in DynamoDB. If you used the AWS SDK's DocumentClient, it might be stored as a Map (M type) instead of a string — adjust the response template accordingly using $util.dynamodb.toJsonObject.
• JSON Scalar: AppSync includes the JSON scalar by default, but if you run into issues, you can explicitly define it in your schema as shown.

内容的提问来源于stack exchange，提问作者Randima Lahiru