ibatis和postgreSQL selectKey

一开始写的是:

<insert id="insertVersion" parameterClass="versionModel">
		begin;
		INSERT INTO
		t_app_version(app_version_id,app_version,app_path,app_sys_type,create_time,modify_time)
		VALUES
		(nextval('t_app_version_app_version_id_seq'),#appVersion#,#appPath#,#appSysType#,LOCALTIMESTAMP,LOCALTIMESTAMP);
		<selectKey resultClass="Integer" keyProperty="appVersionId">
		SELECT currval('t_app_version_app_version_id_seq') as appVersionId;
		</selectKey>
		commit;
	</insert>

这样写是没有问题的，后来改成

<insert id="insertVersion" parameterClass="versionModel">
	begin;
		<selectKey resultClass="Integer" keyProperty="appVersionId">
			SELECT nextval('t_app_version_app_version_id_seq') as appVersionId;
		</selectKey>
		INSERT INTO
		t_app_version(app_version_id,app_version,app_path,app_sys_type,create_time,modify_time)
		VALUES
		(#appVersionId#,#appVersion#,#appPath#,#appSysType#,LOCALTIMESTAMP,LOCALTIMESTAMP);
		commit;
	</insert>

这样就一直报错:org.postgresql.util.PSQLException: ERROR: null value in column "app_version_id" violates not-null constraint

原因是后一种写法先进行了insert，所以id是null，这样的话，就需要把selectKey加上type="pre"，让selectkey在insert之前处理，type="post"代表是之后的处理。