查询表达式非法：在AWS Query的查询中未找到哈希键条件

Question

我在AWS移动中心中有表格，并且正在使用以下模型

public class UserstopcoreDO {
    private String _userId;
    private String _usertoplevel;
    private String _usertopscore;
    private String _username;

    @DynamoDBHashKey(attributeName = "userId")
    @DynamoDBAttribute(attributeName = "userId")
    public String getUserId() {
        return _userId;
    }

    public void setUserId(final String _userId) {
        this._userId = _userId;
    }

    @DynamoDBAttribute(attributeName = "usertoplevel")
    public String getUsertoplevel() {
        return _usertoplevel;
    }

    @DynamoDBAttribute(attributeName = "username")
    public String getUsername() {
        return _username;
    }

    public void setUsername(final String _username) {
        this._username = _username;
    }

    public void setUsertoplevel(final String _usertoplevel) {
        this._usertoplevel = _usertoplevel;
    }

    @DynamoDBIndexHashKey(attributeName = "usertopscore", globalSecondaryIndexName = "usertopscore")
    public String getUsertopscore() {
        return _usertopscore;
    }

    public void setUsertopscore(final String _usertopscore) {
        this._usertopscore = _usertopscore;
    }

}

在表中，我有1500多个记录，现在我想从中获取前10条记录，为此，我编写了以下查询

final DynamoDBQueryExpression<UserstopcoreDO> queryExpression = new DynamoDBQueryExpression<>();
            queryExpression.withLimit(10);
            queryExpression.setScanIndexForward(false);
            final PaginatedQueryList<UserstopcoreDO> results = mapper.query(UserstopcoreDO.class, queryExpression);
            Iterator<UserstopcoreDO> resultsIterator = results.iterator();
            if (resultsIterator.hasNext()) {
                final UserstopcoreDO item = resultsIterator.next();
                try {
                    Log.d("Item :",item.getUsertopscore());
                } catch (final AmazonClientException ex) {
                    Log.e(LOG_TAG, "Failed deleting item : " + ex.getMessage(), ex);
                }
            }

但是当我运行代码时，它给了我一个错误

Caused by: java.lang.IllegalArgumentException: Illegal query expression: No hash key condition is found in the query

但在我的情况下，我不需要任何条件，因为我想获取前10条记录而不是一条特定记录。那么如何处理这种情况呢？

Answer 1

如果您想要“查询”DynamoDB 而不指定所有HashKey，请改用 Scan，即 DynamoDBScanExpression。您可能还想将“usertopscore”更改为 RangeKey 而不是 HashKey。

来自https://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/dynamodbv2/datamodeling/DynamoDBQueryExpression.html每个 DynamoDBQueryExpression 都需要 设置所有哈希键。

另请参阅boto dynamodb2：我可以仅使用范围键查询表吗？

Answer 2

请在查询表达式中设置哈希键。以下是主表和GSI（需要设置索引名称）的查询表达式示例。

查询主表：

设置表的哈希键值。

UserstopcoreDO hashKeyObject = new UserstopcoreDO();
hashKeyObject.setUserId("1");

DynamoDBQueryExpression<UserstopcoreDO> queryExpressionForMainTable = new DynamoDBQueryExpression<UserstopcoreDO>()
    .withHashKeyValues(hashKeyObject);

查询索引：

设置索引名称和索引的哈希键值。

UserstopcoreDO hashIndexKeyObject = new UserstopcoreDO();
    hashIndexKeyObject.setUsertoplevel("100");

DynamoDBQueryExpression<UserstopcoreDO> queryExpressionForGsi = new DynamoDBQueryExpression<UserstopcoreDO>()
            .withHashKeyValues(hashIndexKeyObject).withIndexName("usertopscore");

映射器中的GSI属性：-

@DynamoDBIndexHashKey(attributeName = "usertoplevel",  globalSecondaryIndexName = "usertopscore")
public String getUsertoplevel() {
    return _usertoplevel;
}

@DynamoDBIndexRangeKey(attributeName = "usertopscore", globalSecondaryIndexName = "usertopscore")
public String getUsertopscore() {
    return _usertopscore;
}