How control mybatis‘s localCache? - mybatis

Question

I use mybatis version 3.4.0 in my project with postgre sql. There is a id column
is serial type (auto increate primary key column).
I write the mapper's generateId method to get the serial value:
mapper interface:
public interface DemoTableNameMapper {
long generateId();
...
mapper.xml:
<select id="generateId" resultType="long">
SELECT nextval('"public".demo_table_name_id_seq'::regclass)
</select>
But when I call the mapper's generateId method twice want to get two ID value, I find I get the SAME value!!!
Then I trace into mybatis's source code, I found it's mybatis' localCache return the previous generated ID value.
To work around with this problem, I change my generate's declare and implementation.
interface:
public interface DemoTableNameMapper {
/**
* 产生新的主表的ID
* 注：因在一次事务中需多次调用，需通过混淆参数来避免命中 mybatis 的 localCache
* #return
*/
long generateId(#Param("dummyid") String dummyid);
...
mapper.xml:
<select id="generateId" resultType="long">
SELECT nextval('"public".demo_table_name_id_seq'::regclass)
WHERE #{dummyid}=#{dummyid}
</select>
My question is:
Is there a better way to interact with mybatis's localCache?
I change mapper.xml this way:
<select id="generateId" resultType="long" useCache="false" flushCache="true">
SELECT nextval('"public".demo_table_name_id_seq'::regclass)
</select>
it work!!!

Answer 1

By Default, the localSessionScope is session - So If you make the call twice or N times till the cache clears in the session, it returns you the same value.
If you set localSessionScope as STATEMENT. Every time the new next val is returned.
localCacheScope=STATEMENT
Alternative way is to clear Cache - (make sure if its ok for the performance), after the first call - by calling
clearCache()
Refer Here for complete details - MyBatis Documentation