node.js - 停止 dynamodb 中的重复条目

Question

我在 Dynamodb 中有一个名为 followProduct 的表，它具有以下结构

id - item id
email - user email
product - product id

每当用户关注某个产品时，我都会在表中进行记录。我正在尝试停止重复输入并使用以下代码

let params = {
    TableName: "followProduct",
    ConditionExpression: "email <> :email AND product <> :pid",
    Item: {
        email: "a@a.com",
        product: req.body.productId,
        id: shortid.generate()
    },
    ExpressionAttributeValues: {
        ':email': "a@a.com",
        ":pid": req.body.productId
    }
};
createItemInDDB(params).then(() => {
    res.status(200).send("Company Added");
}, err => {
    console.log(err);
    res.sendStatus(500);
});

CreateItemInDDB 只是一个以参数作为输入并运行文档客户端提供的 put 函数的函数。该参数仍然会产生重复的条目。我希望对于每封电子邮件，每个产品 ID 只能输入一次。

Answer 1

您能描述一下您的表哈希范围键吗？

Dynamodb 只能强制哈希范围表键的唯一性(不适用于全局二级索引键)

来自http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_PutItem.html

To prevent a new item from replacing an existing item, use a conditional expression that contains the attribute_not_exists function with the name of the attribute being used as the partition key for the table. Since every record must contain that attribute, the attribute_not_exists function will only succeed if no matching item exists.

和http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.ConditionExpressions.html :

The PutItem operation will overwrite an item with the same key (if it exists). If you want to avoid this, use a condition expression. This will allows the write to proceed only if the item in question does not already have the same key: