查询特定字段的 dynamodb [英] Query dynamodb for a specific field

问题描述

如何在 dynamodb 中查询匹配特定规则的所有项目?

how do I query dynamodb for all items that match a specific rule?

我正在建立一个在线商店(如 Asos)，并且在 dynamodb 中我有一个产品表.所有产品都有类别"字段.所以我只想做一个简单的查询，我说

I am building an online shop (like Asos) and in dynamodb I have a products table. all of the products have the field 'category'. so I just want to do a simple query whereby I say something like

FROM products WHERE category == 'trainers'

我已经设法让它正常工作，所以我扫描了整个表格并将所有产品归还给我，但我现在想要更具体的查询

I have managed to get it working so I scan the whole table and return me all the products but i want more specific queries now

我假设我想使用类似的东西:KeyConditionExpression 但我在执行此操作时不断收到错误

I assume I want to use something like: KeyConditionExpression but I keep getting an error when I do this

编辑的问题:

代码:

componentDidMount() {
    console.log('mounted');
    const AWS = window.AWS;
    const params = {
      TableName: 'Products',
      FilterExpression: "category = trainers"
    };
...secret key code
ddb.scan(params, (err, data) => {
  if (err) {
    console.log(err, err.stack);
  } else {
    console.log(data);
    this.setState({ products: data })
  }
});

推荐答案

试试这个

 var params = {
  ExpressionAttributeValues: {
   ":catval": {
     S: "trainers"
    }
  }, 
  FilterExpression: "category = :catval", 
  TableName: "Products"
 };
 dynamodb.scan(params, function(err, data) {
  if (err) console.log(err, err.stack);
  else     console.log(data);

您不能在表达式中使用文字.您定义了一个 ExpressionAttributeValue，我将您的名称称为:catval"，但您可以随意称呼它.'S' 表示一个字符串，所以基本上你定义了一个具有 String 类型和值trainers"的 ExpressionAttributeValue.然后，当您应用 FilterExpression 时，您将放入 ExpressionAttributeValue，而不是文字.

You can't use literals in expressions. You define an ExpressionAttributeValue, i've called yours ":catval" but you can call it anything you like. The 'S' means a string, so basically you define an ExpressionAttributeValue with type String and value "trainers". Then when you apply the FilterExpression you put in your ExpressionAttributeValue, not the literal.

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