有一个Table控件，DC的view用的_local，query的语句： <![CDATA[select e from lims_DictItem e where e.category=:category ORDER BY e.sort]]>
category是一个外键，界面上无需显示。做了一个action用于改变order字段的值。代码如下：
@Subscribe(“dictItemsTable.moveUp”)
protected void onItemsTableMoveUpActionPerformed(Action.ActionPerformedEvent event) {
DictItem currentItem = dictItemsTable.getSingleSelected();
if (currentItem==null)
return;
currentItem.setSort(currentItem.getSort()+1);
dataContext.merge(currentItem);
dataContext.commit();
执行的时候，第一次点击按钮是没有问题的，继续点击就直接报错了，category不允许为null。
java.sql.SQLIntegrityConstraintViolationException: Column ‘CATEGORY_ID’ cannot be null
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:117)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:970)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal(ClientPreparedStatement.java:1109)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal(ClientPreparedStatement.java:1057)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeLargeUpdate(ClientPreparedStatement.java:1377)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdate(ClientPreparedStatement.java:1042)
at org.apache.tomcat.dbcp.dbcp2.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:136)
at org.apache.tomcat.dbcp.dbcp2.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:136)
at com.haulmont.cuba.core.sys.jdbc.ProxyPreparedStatement.lambda$executeUpdate$1(ProxyPreparedStatement.java:39)
at com.haulmont.cuba.core.sys.jdbc.ProxyPreparedStatement$$Lambda$232/1138194105.call(Unknown Source)
at com.haulmont.cuba.core.sys.jdbc.ProxyStatement.executeSqlStatement(ProxyStatement.java:257)
at com.haulmont.cuba.core.sys.jdbc.ProxyPreparedStatement.executeUpdate(ProxyPreparedStatement.java:39)
at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeDirectNoSelect(DatabaseAccessor.java:942)
at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeNoSelect(DatabaseAccessor.java:1014)
at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.basicExecuteCall(DatabaseAccessor.java:656)
at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeCall(DatabaseAccessor.java:564)
at org.eclipse.persistence.internal.sessions.AbstractSession.basicExecuteCall(AbstractSession.java:2093)
看了下commit时候的对象，第一次category是null。后面再提交的时候category也是null，但是系统属性有值了，不知道为什么后面提交他就要去更新数据库里的category字段，第一次不会更新。
