java 无法从 DynamoDB 加载数据，因为 List<Object> 类型的属性无法取消转换并使用 @DynamoDBDocument 保存
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Cannot load data from DynamoDB due to an attribute of type List<Object> which is not able to get unconverted and was saved using @DynamoDBDocument
提问by Manthan Jamdagni
I am trying to save a List<CustomObject>using the @DynamoDBDocument but it gives me a DynamoDBMappingException : could not unconvert attribute.
我正在尝试List<CustomObject>使用 @DynamoDBDocument保存一个，但它给了我一个 DynamoDBMappingException : could not unconvert 属性。
Here is what my Entity class looks like -
这是我的实体类的样子 -
@lombok.Data
@DynamoDBTable(tableName = "carTable")
public class Car {
@DynamoDBHashKey(attributeName = "name")
private carName;
@DynamoDBRangeKey(attributeName = "model")
private carModel;
@DynamoDBAttribute(attributeName = "manufacturers")
private List<Manufacturer> manufacturers;
}
The Manufacturer class looks like -
制造商类看起来像 -
@lombok.Data
@DynamoDBDocument
public class Manufacturer {
@DynamoDBAttribute
private String manufacturerName;
}
When using this entity and saving the values into the table it saves properly as JSON, but when retrieving it, an exception is thrown -
使用此实体并将值保存到表中时，它会正确保存为 JSON，但在检索它时，会引发异常 -
com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMappingException: Car[manufacturers]; could not unconvert attribute
at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapperTableModel.unconvert(DynamoDBMapperTableModel.java:271)
[junit] at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.privateMarshallIntoObject(DynamoDBMapper.java:456)
[junit] at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.load(DynamoDBMapper.java:422)
[junit] at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.load(DynamoDBMapper.java:433)
[junit] at com.amazonaws.services.dynamodbv2.datamodeling.AbstractDynamoDBMapper.load(AbstractDynamoDBMapper.java:85)
What am I missing here, do I need to add some sort of TypeConverter or Marshaller here?
我在这里错过了什么，我需要在这里添加某种类型转换器或 Marshaller 吗？
回答by Manthan Jamdagni
A no-args constructer was required to unconvert the attribute, adding @lombok.NoArgsConstructor to the Manufacturer class solved my problem.
需要一个无参数构造函数来取消转换属性，将 @lombok.NoArgsConstructor 添加到制造商类解决了我的问题。
回答by Ivan Mushketyk
I don't think you need a custom converter here, it looks like that DynamoDB has some issues with converting DynamoDB item into a Java object.
我认为您在这里不需要自定义转换器，看起来 DynamoDB 在将 DynamoDB 项目转换为 Java 对象方面存在一些问题。
Check:
查看：
Data in DynamoDB matches your object fields. Check if types are matching as well
What if you define setters explicitly? Maybe Lombok is a culprit here?
DynamoDB 中的数据与您的对象字段相匹配。检查类型是否也匹配
如果您明确定义 setter 会怎样？也许龙目岛是这里的罪魁祸首？
Also it is odd that you do not specify a table name here:
同样奇怪的是，您没有在此处指定表名：
@DynamoDBTable(tableName)
public class Car {
...
}
回答by Rahul Midha
In my case, the issue was that the setters were missing
就我而言，问题是缺少二传手
This was because I was using Lombok with @Builder and @Getter annotations only
这是因为我只使用带有 @Builder 和 @Getter 注释的 Lombok
回答by Sichen Zhao
If you use @Builder, you can still use @Tolerate to add default Constructor
如果您使用@Builder，您仍然可以使用@Tolerate 添加默认构造函数
回答by HelpMatters
In my case, my java class had an attribute as string, whereas dynamodb was storing it as a number. When I changed my attribute to be a intinstead of a string, it worked smoothly.
在我的例子中，我的 java 类有一个作为字符串的属性，而 dynamodb 将它存储为一个数字。当我将我的属性更改为int而不是string 时，它运行顺利。
