插入记录时出现ConstraintViolationException:could not insert 异常

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
   
<hibernate-mapping package="pbc.bz.intendance.model">
   <class name="Intendance" table="t_intendance" >
      <!-- 映射标识属性 -->
      <id name="intendId" column="intend_id" type="java.lang.Integer">
         <generator class="identity" />
      </id>
     
      <!-- 下面映射其他普通属性 -->
      <property name="projectName" column="project_name" type="string" not-null="true" lazy="false" />
      <property name="checkDate"   column="check_date"   type="date"   not-null="true" lazy="false" />
      <property name="transactor"  column="transactor"   type="string" not-null="true" lazy="false" />
      <property name="beChecked"   column="be_checked"   type="string" not-null="true" lazy="false" />
      <property name="problemKind" column="problem_kind"  type="string" not-null="true" lazy="false" />
      <property name="problemDesc" column="problem_desc"  type="text"  not-null="true" lazy="false" />
      <property name="riskKind"    column="risk_kind"    type="string" not-null="true" lazy="false" />
      <property name="controllable" column="controllable"  type="text" not-null="true" lazy="false" />
      <property name="reason"      column="reason"       type="string" not-null="true" lazy="false" />
      <property name="behindDuty"  column="behind_duty"  type="string" not-null="true" lazy="false" />
     
      <!-- 映射该Intendance所关联的User: recorder/rechecker/assessor -->
      <many-to-one name="recorder" column="recorder" class="User" not-null="true" lazy="false" />
      <many-to-one name="rechecker" column="rechecker" class="User" lazy="false" />
      <many-to-one name="assessor" column="assessor" class="User" lazy="false" />
     
      <!-- 映射该Intendance关联的反馈信息Feedback -->
      <many-to-one name="back" column="back_id" class="Feedback" lazy="false" />
      <!-- 映射该Intendance所处的状态State -->
      <many-to-one name="stat" column="state_id" class="State" lazy="false"/>
     
     
      <!-- 配置监督信息Intendance与用户User的映射关系（修改关系－－多对多） -->
      <set name="modifier" table="t_modification_of_intend" lazy="false" inverse="true">
         <key column="intend_id" />
         <one-to-many class="ModificationOfIntendance" />
      </set>
     
      <property name="submitDate" column="submit_date" type="timestamp" not-null="true" lazy="false" />

   </class>
</hibernate-mapping>

// 说明，该action使用了模型驱动方式，即实现了com.opensymphony.xwork2.ModelDriven 接口。

// 添加监督信息
    public String addIntendance() throws Exception {
        Map session = ActionContext.getContext().getSession();
        String ver2 = (String)session.get("randomString");
        session.put("randomString", null);
      
        //
        if (vercode.equalsIgnoreCase(ver2)) {
           
            // 取得当前登录的用户信息
            User cu = (User)session.get("the_user");
            System.out.println("当前User ID: " + cu.getUserId());
           
            model.setRecorder(cu);
            model.setRechecker(null);
            model.setAssessor(null);
            model.setBack(null);
            model.setStat(mgr.getTheState(1));
            model.setSubmitDate(new Date());
           
            System.out.println("*********************");
            System.out.println(model.getStat().getStateId());
            System.out.println(model.getStat().getStateName());
            System.out.println(model.getStat().getStateDesc());
            System.out.println("*********************");
            System.out.println("*********************");
            System.out.println(model.getProjectName());
            System.out.println(model.getCheckDate());
            System.out.println(model.getTransactor());
            System.out.println(model.getBeChecked());
            System.out.println(model.getProblemKind());
            System.out.println(model.getProblemDesc());
            System.out.println(model.getRiskKind());
            System.out.println(model.getControllable());
            System.out.println(model.getReason());
            System.out.println(model.getBehindDuty());
            System.out.println(model.getRecorder().getUserId());
            System.out.println(model.getRechecker());
            System.out.println(model.getAssessor());
            System.out.println(model.getBack());
            System.out.println(model.getStat().getStateId());
            System.out.println(model.getSubmitDate());
           
            System.out.println("*********************");
           
            //return SUCCESS;
           
            if (mgr.addIntendance(model) > 0) {
                addActionMessage("成功添加监督信息！");
                System.out.println("执行到这里了...");
                return SUCCESS;
            }
            else {
                addActionError("添加监督信息失败，请重试！");
                return "failure";
            }
        }
        else {
            addActionError("验证码不匹配，请重新输入！");
            return "failure";
        }
    }

      <!-- 添加监督信息 -->
      <action name="addIntendance"
              class="pbc.bz.intendance.action.IntendanceAction"
              method="addIntendance">
         <result name="input">/intend/addintend.jsp</result>
         <result name="failure">/intend/addintend.jsp</result>
         <result name="success">/users/welcome.jsp</result>
      </action>