DynamoDBMappingException：HASH密钥没有映射 [英] DynamoDBMappingException: no mapping for HASH key

问题描述

在编写DynamoDB Java App时，如果未正确配置表及其数据模型，则在从表进行写入或检索时会收到 HASH键没有映射错误。完整的异常类似于：

When writing a DynamoDB Java App you can receive the 'no mapping for HASH key' error when writing or retrieving from a table if the table and its data model are not configured correctly. The full exception would be similar to:

com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMappingException：< YourClassNameHere> ;;没有哈希键的映射

推荐答案

在此处需要检查两个有用的东西：

Two helpful things to check here:

1）对于您的哈希值的主要设置者，请确保正确设置了 @DynamoDBHashKey 表示法。 @DynamoDBAttribute 不是用于表主哈希键的正确方法， @DynamoDBIndexHashKey 也不正确。

1) For your main setter for your hash key value make sure that the @DynamoDBHashKey notation is correctly set. @DynamoDBAttribute is NOT the correct one to use for your table's main hash key and neither is @DynamoDBIndexHashKey.

2）确保在表定义中定义了哈希键：

2) Make sure that the hash key is defined in the table definition:

        CreateTableRequest createTableRequest = new CreateTableRequest()
                .withTableName("testtable")
                .withKeySchema(
                        new KeySchemaElement("id", KeyType.HASH)
                )
                .withProvisionedThroughput(new ProvisionedThroughput(1L, 1L))
                .withAttributeDefinitions(
                        new AttributeDefinition("id", "S")
                );

        CreateTableResult result = amazonDynamoDB.createTable(createTableRequest);

上面的表定义创建一个表 testtable，其主索引或哈希键变量名为 id ，字符串的类型为 S 。

The above table definition creates a table 'testtable' with a main index or hash key variable titled id and the type is S for string.

另外，如果您使用继承，请确保您没有两个具有相同名称的函数互相覆盖。 Dynamo将使用顶级吸气剂，这可能会导致问题。

Additionally, if you are using inheritance, make sure that you don't have two functions with the same name that override each other. Dynamo will use the top-level getter and this can cause issues.

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