Spring -Mongodb将枚举存储/检索为int而不是字符串 [英] Spring -Mongodb storing/retrieving enums as int not string

问题描述

我的枚举以int形式存储在mongodb中(来自C#应用程序).现在在Java中，当我尝试检索它们时，它将引发异常(似乎只能从字符串值转换为enum).我有什么办法吗?

My enums are stored as int in mongodb (from C# app). Now in Java, when I try to retrieve them, it throws an exception (it seems enum can be converted from string value only). Is there any way I can do it?

另外，当我将一些集合保存到mongodb(来自Java)中时，它会将枚举值转换为字符串(而不是其值/基数).是否有任何覆盖?

Also when I save some collections into mongodb (from Java), it converts enum values to string (not their value/cardinal). Is there any override available?

这可以通过在类级别上编写mongodb-converter来实现，但是我不想为每个类编写mondodb-converter，因为这些枚举在许多不同的类中.

This can be achieved by writing mongodb-converter on class level but I don't want to write mondodb-converter for each class as these enums are in many different classes.

那么我们在现场有什么东西吗?

So do we have something on the field level?

推荐答案

在对spring-mongodb转换器代码进行了长时间的挖掘之后， 好的，我完成了，现在可以正常工作了:)在这里(如果有更简单的解决方案，我也很高兴看到，这就是我所做的):

After a long digging in the spring-mongodb converter code, Ok i finished and now it's working :) here it is (if there is simpler solution i will be happy see as well, this is what i've done ) :

首先定义:

public interface IntEnumConvertable {
      public int getValue();    
}

和一个实现它的简单枚举:

and a simple enum that implements it :

public enum tester implements IntEnumConvertable{   
    vali(0),secondvali(1),thirdvali(5);

    private final int val;
    private tester(int num)
    {
        val = num;          
    }
    public int getValue(){
        return val;
    }
}

好，现在您将需要2个转换器，一个很简单， 另一个比较复杂.简单的方法(这个简单的方法也可以处理简单的转换，并在无法进行强制转换时返回一个字符串，如果您希望将枚举存储为字符串并且将枚举数字存储为整数，则非常有用):

Ok, now you will now need 2 converters , one is simple , the other is more complex. the simple one (this simple baby is also handling the simple convert and returns a string when cast is not possible, that is great if you want to have enum stored as strings and for enum that are numbers to be stored as integers) :

public class IntegerEnumConverters {
    @WritingConverter
    public static class EnumToIntegerConverter implements Converter<Enum<?>, Object> {
        @Override
        public Object convert(Enum<?> source) {
            if(source instanceof IntEnumConvertable)
            {
                return ((IntEnumConvertable)(source)).getValue();
            }
            else
            {
                return source.name();
            }               
        }
    }   
 }

更复杂的一个实际上是转换器工厂:

the more complex one , is actually a converter factory :

public class IntegerToEnumConverterFactory implements ConverterFactory<Integer, Enum> {
        @Override
        public <T extends Enum> Converter<Integer, T> getConverter(Class<T> targetType) {
            Class<?> enumType = targetType;
            while (enumType != null && !enumType.isEnum()) {
                enumType = enumType.getSuperclass();
            }
            if (enumType == null) {
                throw new IllegalArgumentException(
                        "The target type " + targetType.getName() + " does not refer to an enum");
            }
            return new IntegerToEnum(enumType);
        }
        @ReadingConverter
        public static class IntegerToEnum<T extends Enum>  implements Converter<Integer, Enum> {
            private final Class<T> enumType;

            public IntegerToEnum(Class<T> enumType) {
                this.enumType = enumType;
            }

            @Override
            public Enum convert(Integer source) {
                  for(T t : enumType.getEnumConstants()) {
                      if(t instanceof IntEnumConvertable)
                      {
                          if(((IntEnumConvertable)t).getValue() == source.intValue()) {
                                return t;
                            }                         
                      }                     
                    }
                    return null;   
            }
        }
}

现在对于hack部分，我个人没有找到任何编程方式"在mongoConverter中注册转换器工厂，因此我在代码中进行了一点点铸造，在这里(将这2个婴儿函数放在您的@Configuration类)

and now for the hack part , i personnaly didnt find any "programmitacly" way to register a converter factory within a mongoConverter , so i digged in the code and with a little casting , here it is (put this 2 babies functions in your @Configuration class)

      @Bean
        public CustomConversions customConversions() {
            List<Converter<?, ?>> converters = new ArrayList<Converter<?, ?>>();
            converters.add(new IntegerEnumConverters.EnumToIntegerConverter());     
// this is a dummy registration , actually it's a work-around because
// spring-mongodb doesnt has the option to reg converter factory.
// so we reg the converter that our factory uses. 
converters.add(new IntegerToEnumConverterFactory.IntegerToEnum(null));      
            return new CustomConversions(converters);
        }

    @Bean
    public MappingMongoConverter mappingMongoConverter() throws Exception {
        MongoMappingContext mappingContext = new MongoMappingContext();
        mappingContext.setApplicationContext(appContext);
        DbRefResolver dbRefResolver = new DefaultDbRefResolver(mongoDbFactory());
        MappingMongoConverter mongoConverter = new MappingMongoConverter(dbRefResolver, mappingContext);        
        mongoConverter.setCustomConversions(customConversions());       
        ConversionService convService = mongoConverter.getConversionService();
        ((GenericConversionService)convService).addConverterFactory(new IntegerToEnumConverterFactory());                  
        mongoConverter.afterPropertiesSet();
        return mongoConverter;
    } 

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