我正在尝试查询DynamoDB表以查找未设置 email
属性的所有项目 . 表中存在一个名为 EmailPasswordIndex
的全局二级索引,其中包含 email
字段 .
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));
});
2 Answers
如果该字段不存在,则@jaredHatfield是正确的,但如果该字段为空则不起作用 . NULL是关键字,不能直接使用 . 但您可以将它与ExpressionAttributeValues一起使用 .
DynamoDB的全局二级索引允许索引稀疏 . 这意味着如果您有一个GSI,其项目的散列或范围键未定义,那么该项目将不会包含在GSI中 . 这在许多用例中很有用,因为它允许您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,这种方法将无法工作 .
要获得所有未设置字段的项目,您可能需要使用过滤器进行扫描 . 此操作将非常昂贵,但它将是直截了当的代码,如下所示: