AWS DynamoDB QueryRequest 多个排序键值

Question

我有以下数据

分区键	排序键	价值
啊	str1	1
啊	str2	123
啊	str3	122
ab	str1	12
ab	str3	111
ac	str1	112

通过使用

QueryRequest

，我想选择分区键为“aa”且排序键为“str1”或“str3”的条目。我尝试创建一个

Condition

，但是对于不同的异常没有任何作用，所以有人可以指出如何编写这个查询吗？

var pkCondition = new Condition
{
    ComparisonOperator = ComparisonOperator.EQ,
    AttributeValueList =
    {
        new AttributeValue { S = "aa" },
    },
};

// Exception One or more parameter values were invalid: Condition parameter type does not match schema type
var skCondition1 = new Condition
{
    ComparisonOperator = ComparisonOperator.EQ,
    AttributeValueList =
    {
        new AttributeValue { SS = { "str1", "str3" } },
    },
};

// Exception: One or more parameter values were invalid: Invalid number of argument(s) for the EQ ComparisonOperator
var skCondition2 = new Condition
{
    ComparisonOperator = ComparisonOperator.EQ,
    AttributeValueList =
    {
        new AttributeValue { S = "str1" },
        new AttributeValue { S = "str3" },
    },
};

// Well this one is clear because IN cannot be performed on keys
// Exception: One or more parameter values were invalid: ComparisonOperator IN is not valid for SS AttributeValue type
var skCondition3 = new Condition
{
    ComparisonOperator = ComparisonOperator.IN,
    AttributeValueList =
    {
        new AttributeValue { SS = { "str1", "str3" } },
    },
};

// Works, but not what I need
var skCondition4 = new Condition
{
    ComparisonOperator = ComparisonOperator.EQ,
    AttributeValueList =
    {
        new AttributeValue { S = "str1" },
    },
};

return new QueryRequest
{
    TableName = "My table",
    KeyConditions =
    {
        { "Partition key", pkCondition },
        { "Sort key", skCondition },
    },
};

经过一些研究，我发现

KeyConditionExpression

也可以使用，但我还没有找到任何适合我的情况的组合。

// Exception: Invalid operator used in KeyConditionExpression: OR
const string keyConditionExpression1 = "#pk = :pkval AND (#sk = :sk1 OR #sk = :sk2)";

// Exception: Invalid operator used in KeyConditionExpression: IN
const string keyConditionExpression2 = "#pk = :pkval AND #sk IN (:sk1, :sk2)";

new QueryRequest
{
    TableName = "My table",
    KeyConditionExpression = keyConditionExpression,
    ExpressionAttributeNames = new Dictionary<string, string>
    {
        { "#pk", "Partition key" },
        { "#sk", "Sort key" },
    },
    ExpressionAttributeValues = new Dictionary<string, AttributeValue>
    {
        { ":pkval", new AttributeValue { S = "aa" } },
        { ":sk1", new AttributeValue { S = "str1" } },
        { ":sk2", new AttributeValue { S = "str3" } },
    },
};

接下来，我还尝试使用

FilterExpression

，其中允许 IN 和 OR，但又出现了另一个例外：

Filter Expression can only contain non-primary key attributes

。

new QueryRequest
{
    TableName = "My table",
    KeyConditionExpression = "#pk = :pkval",
    FilterExpression = "#sk IN (:sk1, :sk2)",
    ExpressionAttributeNames = new Dictionary<string, string>
    {
        { "#pk", "Partition key" },
        { "#sk", "Sort key" },
    },
    ExpressionAttributeValues = new Dictionary<string, AttributeValue>
    {
        { ":pkval", new AttributeValue { S = "aa" } },
        { ":sk1", new AttributeValue { S = "str1" } },
        { ":sk2", new AttributeValue { S = "str3" } },
    },
};

Answer 1

DynamoDB 数据结构可以比作 B 树。也就是说，一个高效的 Query 只读取一条连续的数据。

您的访问模式无法保证数据是连续的并且在磁盘上彼此相邻存储。这就是你挣扎的原因。

可能的解决方案

• 根据您存储在排序键中的实际数据，您可以执行

  between

  或

  begins_with

  条件。 `(str1,str3) 之间的 SK。

• 但是，您的访问模式似乎表明您需要不遵循模式的特定排序键，在这种情况下，您应该使用

  BatchGetItem

  ，它允许您每个请求最多获取 100 个项目。

• 如果排序键的完整值未知，那么您可以执行一个

  ExecuteStatement

  请求，该请求将在后台执行多个查询调用，以满足您的访问模式。