[GitHub] [incubator-shardingsphere] fenghuanfun opened a new issue #3742: ComplexKeysShardingAlgorithm> Actual Use Suggestion

[GitBox <gi...@apache.org>]

fenghuanfun opened a new issue #3742: ComplexKeysShardingAlgorithm<T extends Comparable<?>> Actual Use Suggestion
URL: https://github.com/apache/incubator-shardingsphere/issues/3742
 
 
   ## Feature Request
   ### Is your feature request related to a problem?
    - I report a bug in an issue, and it's version is ` sharding-jdbc-core:4.0.0-RC1 `
   [ComplexKeysShardingAlgorithm ClassCastException](https://github.com/apache/incubator-shardingsphere/issues/2613)
   - now it hava been fixed in  ` sharding-jdbc-core:4.0.0-RC3 `
   - However, i dont think it is the right way to resove this problem
   - example, in this ` ShardingAlgorithm ` 
   ```java
   public class BaseComplexKeysShardingAlgorithm implements ComplexKeysShardingAlgorithm<Timestamp> {
       @Override
       public Collection<String> doSharding(Collection<String> availableTargetNames, ComplexKeysShardingValue<Timestamp> shardingValue) {
           Range<Timestamp> range = shardingValue.getColumnNameAndRangeValuesMap().get("create_time");
           Timestamp timestamp = range.upperEndpoint();
           System.out.println(timestamp);
           return availableTargetNames;
       }
   }
   ```
         the field 'create_time' type is datetime(6) in mysql, java.sql.Timestamp in Java Entity
   - if the sql is ` select * from t_order where create_time = '2019-12-01 00:00:00.000000' ;`
    the `ShardingAlgorithm ` will receive a sharingValue that instance of Timestamp. 
   No problem so far.
   - However, if i use mysql function like `date_format`, the sql change to ` select * from t_order where date_fromat(create_time,'%Y-%m-%d') = '2019-12-01' ;` 
    it will receive ` ClassCastException` again when i try to get the sharding value. because the sharding value's type is `java.lang.String` indeed
   
   ### Describe the feature you would like.
   - in this sample, i think this situation exist in other mysql function too
   - so i suggest that `sharding-jdbc` should not just add a GenericType on `org.apache.shardingsphere.api.sharding.complex.ComplexKeysShardingAlgorithm<T extends Comparable<?>>`. 
   - GenericType limit that one field only have one type in a `ShardingAlgorithm`
   - Looking forward to your reply, thank you

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