Support dynamic SQL provider [DATAJDBC-319]

Sanghyuk Jung opened DATAJDBC-319 and commented

In MyBatis, Dynamic sql is supported by @SelectProvider

http://kamalmeet.com/java/mybatis-using-selectprovider-and-resultmap/ ( updated link)

It would be more convenient if a similar feature is in Spring Data JDBC

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No further details from DATAJDBC-319

[chenjianjx]

+1

[spring-projects-issues]

Sanghyuk Jung commented

As I mentioned, MyBatis supports a similar feature, it can be a reference.

Following examples are from http://www.mybatis.org/mybatis-3/java-api.html .

@SelectProvider(type = UserSqlBuilder.class, method = "buildGetUsersByName")
List<User> getUsersByName(
    @Param("name") String name, @Param("orderByColumn") String orderByColumn);

class UserSqlBuilder {

  // If not use @Param, you should be define same arguments with mapper method
  public static String buildGetUsersByName(
      final String name, final String orderByColumn) {
    return new SQL(){{
      SELECT("*");
      FROM("users");
      WHERE("name like #{name} || '%'");
      ORDER_BY(orderByColumn);
    }}.toString();
  }

  // If use @Param, you can define only arguments to be used
  public static String buildGetUsersByName(@Param("orderByColumn") final String orderByColumn) {
    return new SQL(){{
      SELECT("*");
      FROM("users");
      WHERE("name like #{name} || '%'");
      ORDER_BY(orderByColumn);
    }}.toString();
  }
}

The implementation of MyBatis is at https://github.com/mybatis/mybatis-3/blob/master/src/main/java/org/apache/ibatis/builder/annotation/ProviderSqlSource.java#L106

The ways of MyBatis has the disadvantage of weak inspection at the time of compilation.

An alternative is to define a stricter interface , as shown below.

//  This interface is assumed to be provided by Spring Data JDBC.
public interface QueryProvider {
    String getQuery(SqlParameterSource source);

    default boolean isNotNull(SqlParameterSource source, String paramName){
        return source.hasValue(paramName) && (source.getValue(paramName) != null);
    }
    // Another helper methods can be added as default methods, for example 'isNotEmpty()'
}


// An  implementation class of QueryProvider by the framework user
public class ProductQueryProvider implements QueryProvider {
    @Override
    public String getQuery(SqlParameterSource source) {
        String sql = "SELECT id name FROM product";
        if (isNotNull(source, "name")) {
            return sql + " WHERE name = :name";
        }
        return sql;
    }
}

//  The QueryProvider's implementation class is specified in the Repository interface, similar to the RowMapper's implementation class.

public interface ProductRepository extends CrudRepository<Product, String> {
       @Query(rowMapper=ProducMapper.class, queryProvider = productSelectProvider.class)
	List<Product> findByName(@Param("name") String name);
}

When infrastructure for semantic SQL generation ( https://jira.spring.io/browse/DATAJDBC-309) is merged in the future, this feature will create a larger synergy.

If the specifications are confirmed here, I am willing to send pull request