如何在DynamoDB中查询不存在的(null)属性 [英] How do you query for a non-existent (null) attribute in DynamoDB
问题描述
我正在尝试查询DynamoDB表,以查找未设置电子邮件
属性的所有项目。包含 email
字段的表上存在一个名为 EmailPasswordIndex
的全局二级索引。
I'm trying to query a DynamoDB table to find all items where the email
attribute is not set. A global secondary index called EmailPasswordIndex
exists on the table which includes the email
field.
var params = {
"TableName": "Accounts",
"IndexName": "EmailPasswordIndex",
"KeyConditionExpression": "email = NULL",
};
dynamodb.query(params, function(err, data) {
if (err)
console.log(JSON.stringify(err, null, 2));
else
console.log(JSON.stringify(data, null, 2));
});
结果:
{
"message": "Invalid KeyConditionExpression: Attribute name is a reserved keyword; reserved keyword: NULL",
"code": "ValidationException",
"time": "2015-12-18T05:33:00.356Z",
"statusCode": 400,
"retryable": false
}
表定义:
var params = {
"TableName": "Accounts",
"KeySchema": [
{ "AttributeName": "id", KeyType: "HASH" }, // Randomly generated UUID
],
"AttributeDefinitions": [
{ "AttributeName": "id", AttributeType: "S" },
{ "AttributeName": "email", AttributeType: "S" }, // User e-mail.
{ "AttributeName": "password", AttributeType: "S" }, // Hashed password.
],
"GlobalSecondaryIndexes": [
{
"IndexName": "EmailPasswordIndex",
"ProvisionedThroughput": {
"ReadCapacityUnits": 1,
"WriteCapacityUnits": 1
},
"KeySchema": [
{ "AttributeName": "email", KeyType: "HASH" },
{ "AttributeName": "password", KeyType: "RANGE" },
],
"Projection": { "ProjectionType": "ALL" }
},
],
ProvisionedThroughput: {
ReadCapacityUnits: 1,
WriteCapacityUnits: 1
}
};
dynamodb.createTable(params, function(err, data) {
if (err)
console.log(JSON.stringify(err, null, 2));
else
console.log(JSON.stringify(data, null, 2));
});
推荐答案
DynamoDB的全局二级索引允许稀疏索引。这意味着,如果您有一个GSI,但未定义该项目的哈希或范围键,则该项目将不会直接包含在GSI中。这在许多用例中很有用,因为它使您可以直接识别包含某些字段的记录。但是,如果您正在寻找缺少字段的方法,这种方法将行不通。
DynamoDB's Global Secondary Indexes allow for the indexes to be sparse. That means that if you have a GSI whose hash or range key for an item is not defined then that item will simply not be included in the GSI. This is useful in a number of use cases as it allows you to directly identify records that contain certain fields. However, this approach will not work if you are looking for the lack of a field.
要获得所有未设置字段的项目,最好的选择是借助过滤器进行扫描。此操作将非常昂贵,但代码很简单,如下所示:
To get all of the items that have a field not set your best bet may be resorting to a scan with a filter. This operation will be very expensive but it would be straightforward code looking something like the following:
var params = {
TableName: "Accounts",
FilterExpression: "attribute_not_exists(email)"
};
dynamodb.scan(params, {
if (err)
console.log(JSON.stringify(err, null, 2));
else
console.log(JSON.stringify(data, null, 2));
});
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