如何将项目添加到列表？

Question

我想在我的用户 table 中的 listOfVideosRated[] 列表中添加一个字符串词。

Answer 1

如果您可以 post 您的模式/解析器映射模板，我可以提供更具体的建议，但我会尽我最大的努力回答您目前已 post 的内容。

简单方法

如果您已经有了现有的项目，一种方法是更新现有的 Pairs 并将其传递给您现有的 mutation。

const existingItem = {
  id: "e5eb02ae-04d5-4331-91e6-11efaaf12ea5",
  Pairs: [['a', 'b'],['c', 'd'],['e', 'f']]
}

const newPairs = {
  number1: "g",
  number2: "h"
}

const updateinfo = {
  id: existingItem.id,
  // Note that if existingItem.Pairs is always defined this can be simplified to
  // Pairs: [...existingItem.Pairs, [newPairs.number1, newPairs.number2]]
  Pairs: existingItem.Pairs ?
      [...existingItem.Pairs, [newPairs.number1, newPairs.number2]] : 
      [[newPairs.number1, newPairs.number2]]
}

try {
  await API.graphql(graphqlOperation (UpdateInfo, { input: updateinfo }))  
  //mutation
  console.log('success')
} 
catch (err) {
  console.log(err)
}

使用 DynamoDB 函数

如果您没有现有的项目或者如果 Pairs 可以相当大，可以使用 AWS DynamoDB 的 list_append 函数代替。

list_append (operand, operand)

This function evaluates to a list with a new element added to it. You can append the new element to the start or the end of the list by reversing the order of the operands.

这是一个使用它的特定突变的示例。

### SDL
type Item {
    id: ID!
    Pairs: [[String]]
}

input AddPairInput {
    id: ID!
    number1: String!
    number2: String!
}

type Mutation {
    addPairToItem(input: AddPairInput!): Item!
}

...rest of schema omitted for brevity 

### Resolver Request Mapping Template
{
    "version": "2017-02-28",
    "operation": "UpdateItem",
    "key": {
        "id": { "S": "$ctx.args.input.id"}
    },
    "update": {
        ### Note: we also use if_not_exists here so this works if Pairs is not yet defined on the item.
        "expression":"SET Pairs = list_append(if_not_exists(Pairs, :emptyList), :newPair)",
        "expressionValues": 
          { 
            ":newPair":{"L": [{"L":[{"S":"$ctx.args.input.number1"},
                                    {"S":"$ctx.args.input.number2"}]}]},
            ":emptyList":{"L": []}
          }
        }
}

### Resolver Response Mapping Template
$util.toJson($ctx.result)

这种方式也很好，因为如果其他人更新了 Pairs，您将不会覆盖他们的更新。您还可以通过反转 list_append 函数的参数顺序将新的 Pair 添加到列表的开头。

DynamoDB 函数与 AWS Amplify

如果您的项目是由 AWS Amplify 生成的，您将需要添加 a customer resolver.

第 1 步：向您的架构添加新的变更

### ./amplify/backend/api/<api_name>/schema.graphql
type Item @model {
  id: ID!
  Pairs: [[String]]
}

type Mutation {
  addPairToItem(input: AddPairToItemInput!): Item!
}

input AddPairToItemInput {
  id: ID!
  number1: String!
  number2: String!
}

第 2 步：添加解析器请求映射模板

### ./amplify/backend/api/<api_name>/resolvers/Mutation.addPairToItem.req.vtl
{
    "version": "2017-02-28",
    "operation": "UpdateItem",
    "key": {
        "id": { "S": "$ctx.args.input.id"}
    },
    "update": {
        "expression":"SET Pairs = list_append(if_not_exists(Pairs, :emptyList), :newPair)",
        "expressionValues":
          {
            ":newPair":{"L": [{"L":[{"S":"$ctx.args.input.number1"},{"S":"$ctx.args.input.number2"}]}]},
            ":emptyList":{"L": []}
          }
        }
}

第 3 步：添加解析器响应映射模板

### ./amplify/backend/api/<api_name>/resolvers/Mutation.addPairToItem.res.vtl
$util.toJson($ctx.result)

第 4 步：将您的自定义解析器添加到您的 CustomResources 堆栈

### ./amplify/backend/api/<api_name>/stacks/CustomResources.json
    "Resources": {
        // ...other resources may exist here
        "AddPairToItemResolver": {
            "Type": "AWS::AppSync::Resolver",
            "Properties": {
                "ApiId": {
                    "Ref": "AppSyncApiId"
                },
                "DataSourceName": "ItemTable",
                "TypeName": "Mutation",
                "FieldName": "addPairToItem",
                "RequestMappingTemplateS3Location": {
                    "Fn::Sub": [
                        "s3://${S3DeploymentBucket}/${S3DeploymentRootKey}/resolvers/Mutation.addPairToItem.req.vtl",
                        {
                            "S3DeploymentBucket": {
                                "Ref": "S3DeploymentBucket"
                            },
                            "S3DeploymentRootKey": {
                                "Ref": "S3DeploymentRootKey"
                            }
                        }
                    ]
                },
                "ResponseMappingTemplateS3Location": {
                    "Fn::Sub": [
                        "s3://${S3DeploymentBucket}/${S3DeploymentRootKey}/resolvers/Mutation.addPairToItem.res.vtl",
                        {
                            "S3DeploymentBucket": {
                                "Ref": "S3DeploymentBucket"
                            },
                            "S3DeploymentRootKey": {
                                "Ref": "S3DeploymentRootKey"
                            }
                        }
                    ]
                }
            }
        }
    },

第 5 步：构建和部署您的新更改

运行 amplify api gql-compile 查看生成的代码中的新更改（可选）。
运行 amplify push 部署您的更改。

现在您可以运行 amplify api console 或使用新生成的代码来测试新突变的变化。

要生成新代码，您可以运行 amplify codegen。然后你应该能够做这样的事情

import Amplify, { API, graphqlOperation } from "aws-amplify";
import * as mutations from './graphql/mutations';

// Mutation
const addPairToItem = {
    id: '1',
    number1: 'a',
    number2: 'b'
};

const newItem = await API.graphql(graphqlOperation(mutations.addPairToItem, {input: addPairToItem}));

其他示例

记得用您添加的任何新解析器更新您的 CustomResources.json 文件。

将单个项目添加到标量值列表

### ./amplify/backend/api/<api_name>/schema.graphql
type Item @model {
    id: ID!
    words: [String]
}

input AddWordInput {
    id: ID!
    word: String!
}

type Mutation {
    addWordToItem(input: AddWordInput!): Item!
}

### ./amplify/backend/api/<api_name>/resolvers/Mutation.addWordToItem.req.vtl
{
    "version": "2017-02-28",
    "operation": "UpdateItem",
    "key": {
        "id": { "S": "$ctx.args.input.id"}
    },
    "update": {
        "expression":"SET words = list_append(if_not_exists(words, :emptyList), :newWord)",
        "expressionValues":
          {
            ":newWord":{"L": [{"S":"$ctx.args.input.word"}]},
            ":emptyList":{"L": []}
          }
        }
}

### ./amplify/backend/api/<api_name>/resolvers/Mutation.addWordToItem.res.vtl
$util.toJson($ctx.result)


### Usage
import Amplify, { API, graphqlOperation } from "aws-amplify";
import * as mutations from './graphql/mutations';

// Mutation
const newWord = {
    id: '1',
    word: 'foo'
};

const newItem = await API.graphql(graphqlOperation(mutations.addWordToItem, {input: newWord}));

将多项添加到标量值列表

注意：我在这里介绍 $util.dynamodb.toDynamoDBJson 是为了让构建我们的 VTL 更容易。到目前为止，我一直很明确，但这个实用程序可以简化很多工作。 More here

### ./amplify/backend/api/<api_name>/schema.graphql
type Item @model {
    id: ID!
    words: [String]
}

input AddWordsInput {
  id: ID!
  words: [String!]!
}

type Mutation {
  addWordsToItem(input: AddWordsInput!): Item!
}

### ./amplify/backend/api/<api_name>/resolvers/Mutation.addWordsToItem.req.vtl
{
    "version": "2017-02-28",
    "operation": "UpdateItem",
    "key": {
        "id": { "S": "$ctx.args.input.id"}
    },
    "update": {
        "expression":"SET words = list_append(if_not_exists(words, :emptyList), :newWords)",
        "expressionValues":
          {
            ":newWords": $util.dynamodb.toDynamoDBJson($ctx.args.input.words),
            ":emptyList": $util.dynamodb.toDynamoDBJson([])
          }
        }
}

### ./amplify/backend/api/<api_name>/resolvers/Mutation.addWordsToItem.res.vtl
$util.toJson($ctx.result)


### Usage
import Amplify, { API, graphqlOperation } from "aws-amplify";
import * as mutations from './graphql/mutations';

// Mutation
const newWords = {
    id: '1',
    words: ["bar","xyz","bar"]
};

const newItem = await API.graphql(graphqlOperation(mutations.addWordsToItem, {input: newWords}));

从标量值列表中删除一个项目

从 DynamoDB 的列表中删除元素是 done using the REMOVE action。您必须指定 non-negative 索引作为更新表达式的一部分。如果项目上不存在索引，您的请求不会失败（例如没有索引越界异常）。

type Item @model {
    id: ID!
    words: [String]
}

input RemoveWordInput {
  id: ID!
  wordIndex: Int!
}

type Mutation {
    removeWordFromItem(input: RemoveWordInput!): Item!
}

### ./amplify/backend/api/<api_name>/resolvers/Mutation.removeWordFromItem.req.vtl
{
    "version": "2017-02-28",
    "operation": "UpdateItem",
    "key": {
        "id": { "S": "$ctx.args.input.id"}
    },
    "update": {
        "expression":"REMOVE words[$ctx.args.input.wordIndex]"
    }
}

### ./amplify/backend/api/<api_name>/resolvers/Mutation.removeWordFromItem.res.vtl
$util.toJson($ctx.result)


### Usage
import Amplify, { API, graphqlOperation } from "aws-amplify";
import * as mutations from './graphql/mutations';

// Mutation
const removeWord = {
    id: '1',
    // The index is 0 based so wordIndex: 0
    // would delete the first item,
    // wordIndex: 1 deletes the second, etc.
    wordIndex: 1 
};

const newItem = await API.graphql(graphqlOperation(mutations.removeWordFromItem, {input: removeWord}));

如何将项目添加到列表？

How do i add items to a list?

javascript

database

amazon-dynamodb

graphql

aws-appsync