Javascript DynamoDB 中的 Scan 函数,保留关键字为 FilterExpression NodeJS
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Scan Function in DynamoDB with reserved keyword as FilterExpression NodeJS
提问by Saleem Ahmed
My scan function :
我的扫描功能:
var tableName = 'faasos_orders',
filterExp = 'status = :delivered OR status = :void OR status = :bad',
projectionValues = '',
expressionAttr = {};
expressionAttr[":delivered"] = "delivered";
expressionAttr[":bad"] = "bad";
expressionAttr[":void"] = "void";
limit = 10;
dynamoConnector.getItemUsingScan(tableName, filterExp, projectionValues, expressionAttr, function (err, data) { ...........}
Error on running :
运行时出错:
{ [ValidationException: Invalid FilterExpression: Attribute name is a reserved keyword; reserved keyword: status]
message: 'Invalid FilterExpression: Attribute name is a reserved keyword; reserved keyword: status',
code: 'ValidationException',
time: Mon Apr 18 2016 21:57:30 GMT+0530 (IST),
requestId: 'AV6QFHM7SPQT1QR3D4OO81ED4FVV4KQNSO5AEMVJF66Q9ASUAAJG',
statusCode: 400,
retryable: false,
retryDelay: 0 }
Now I do get the point I am trying to use a reserved keyword in th e filterExpression which is illegal. But if I run the same function through aws gui it returns data beautifully (check image for details): Scan function on status through gui
现在我明白了,我试图在过滤器表达式中使用一个非法的保留关键字。但是如果我通过 aws gui 运行相同的函数,它会很好地返回数据(查看图像了解详细信息): 通过 gui 扫描状态函数
So the question is how do I add the filter expression through node without having to change the key name ???
所以问题是如何通过节点添加过滤器表达式而不必更改键名???
回答by Saleem Ahmed
Solved :
解决了 :
There are two parameters taken by aws-sdk :
aws-sdk 有两个参数:
Expression Attribute Name
表达式属性名称
Expression Attribute Value
表达式属性值
both provide the functionality of replacing placeholders used in the attributes list. Here by Attributes it is a bit ambiguous, where I got confused. The wizards over at aws mean both the key and value when they use the term attribute.
两者都提供替换属性列表中使用的占位符的功能。这里的 Attributes 有点模棱两可,让我感到困惑。aws 上的向导在使用术语属性时表示键和值。
So in a case where you want to use a reserved key word as a key attribute use the Expression Attribute Name parameter with #(pound) to denote the placeholder.
因此,如果您想使用保留关键字作为关键属性,请使用带有 #(pound) 的 Expression Attribute Name 参数来表示占位符。
Similarly where you want to use placeholders for value attribute use the Expression Attribute Value parameter with :(colon) to denote the placeholder.
类似地,您要为 value 属性使用占位符,请使用带有 :(colon) 的 Expression Attribute Value 参数来表示占位符。
So finally my code (working) looks like this :
所以最后我的代码(工作)看起来像这样:
var param = {
TableName: "faasos_orders",
FilterExpression: "#order_status = :delivered OR #order_status = :void OR #order_status = :bad",
ExpressionAttributeValues: {
":delivered": "delivered",
":void": "void",
":bad": "bad"
}
ExpressionAttributeNames: {
"#order_status": "status"
}
};
dynamodb.scan(param, function (err, data) {....});
回答by Mark B
:status
is a placeholder in your expression that you aren't providing a value for. See how you are providing values for your other placeholders here:
:status
是表达式中的占位符,您没有为其提供值。在此处查看您如何为其他占位符提供值:
expressionAttr[":delivered"] = "delivered";
expressionAttr[":bad"] = "bad";
expressionAttr[":void"] = "void"
You need to do the same for the :status
placeholder. I don't see anything about a reserved word in the error message, so I'm not sure why you think that's the cause of the error. The error very specifically states that you aren't providing a value for the :status
placeholder.
您需要对:status
占位符执行相同的操作。我在错误消息中没有看到任何关于保留字的信息,所以我不确定为什么你认为这是错误的原因。该错误非常明确地指出您没有为:status
占位符提供值。