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RDS 解析程序映射模板参考
这些区域有:Amazon AppSync利用 RDS 解析程序映射模板,开发人员可将 SQL 查询发送到 Amazon Aurora Serverless 数据 API,并获取这些查询的结果。
请求映射模板
RDS 请求映射模板相当简单:
{ "version": "2018-05-29", "statements": [], "variableMap": {} }
下面是 RDS 请求映射模板的 JSON 架构表示形式(解析后):
{ "definitions": {}, "$schema": "https://json-schema.org/draft-07/schema#", "$id": "https://example.com/root.json", "type": "object", "title": "The Root Schema", "required": [ "version", "statements", "variableMap" ], "properties": { "version": { "$id": "#/properties/version", "type": "string", "title": "The Version Schema", "default": "", "examples": [ "2018-05-29" ], "enum": [ "2018-05-29" ], "pattern": "^(.*)$" }, "statements": { "$id": "#/properties/statements", "type": "array", "title": "The Statements Schema", "items": { "$id": "#/properties/statements/items", "type": "string", "title": "The Items Schema", "default": "", "examples": [ "SELECT * from BOOKS" ], "pattern": "^(.*)$" } }, "variableMap": { "$id": "#/properties/variableMap", "type": "object", "title": "The Variablemap Schema" } } }
以下是带静态查询的请求映射模板示例:
{ "version": "2018-05-29", "statements": [ "select title, isbn13 from BOOKS where author = 'Mark Twain'" ] }
版本
版本字段对于所有请求映射模板都相同,它用来定义模板使用的版本。版本字段为必填字段。值为 “2018-05-29” 是 Amazon RDS 映射模板唯一支持的版本。
"version": "2018-05-29"
语句
语句数组是开发人员提供的查询的占位符。目前,每个请求映射模板最多支持两个查询。以下是可能的:
{ "version": "2018-05-29", "statements": [ $util.toJson("insert into BOOKS VALUES ('$ctx.args.newBook.author', '$ctx.args.newBook.title', '$ctx.args.newBook.ISBN13')"), $util.toJson("select * from BOOKS WHERE isbn13 = '$ctx.args.newBook.isbn13'") ] }
Amazon AppSync每个请求映射模板最多支持两个语句。
VariableMap
variableMap 是一个可选字段,它包含可用于使 SQL 语句更短且更易读的别名。例如,以下是可能的:
{ "version": "2018-05-29", "statements": [ "insert into BOOKS VALUES (:AUTHOR, :TITLE, :ISBN13)", "select * from BOOKS WHERE isbn13 = :ISBN13" ], "variableMap": { ":AUTHOR": $util.toJson($ctx.args.newBook.author), ":TITLE": $util.toJson($ctx.args.newBook.title), ":ISBN13": $util.toJson($ctx.args.newBook.isbn13) } }
Amazon AppSync将使用变量映射值构造发送到 Amazon Aurora Serverless 数据 API 的查询。例如,两个查询Amazon AppSync将发送到 Amazon RDS 将是(假设“$ctx.args.newBook.author"='Mark Twain'
、"$ctx.args.newBook.title"='Adventures of Huckleberry Finn'
和"$ctx.args.newBook.isbn13"='978-1948132817'
):
INSERT INTO BOOKS VALUES ('Mark Twain', 'Adventures of Huckleberry Finn', '978-1948132817');
和
SELECT from BOOKS where isbn13='978-1948132817';