Code点火器3.0.1:从选择和输入中获取值

我有一个"select"类别选项，用户可以从中选择不同的选项，如果用户选择"其他"，则会出现一个输入字段（以便用户可以添加另一个类别），并在该类别下发布文章
我取select的值，并检查输入是否为空，然后更新我有select值的同一变量
现在的问题是，我似乎无法在"选择选项和输入"字段之间切换，如果我只从选择选项中选择值，效果很好，但当用户选择"其他"并为输入字段指定一个新类别时，变量保持select值
当我们尝试通过输入字段添加时，会出现以下错误：

错误编号：1452
无法添加或更新子行：外键约束失败（ci.user_articles，constraint article_catagory_fk foreign key（cat_id_fk）REFERENCES catagory（cat_id）ON DELETE NO ACTION update CASCADE）
INSERT INTO user_articles（cat_id_fk、title、article）VALUES（"others"、"New title"、"我的文章是棉花糖"）；

这是我在Model_article.php文件中的add_article（）函数：

public function add_article()
{
        $id = $this->input->post('hiddenValue');
        $title = $this->input->post('title');
        $catagory_id = $this->input->post('catagory_select');
        $cat = $this->input->post('cat');
        if (!isset($cat))
        {
            $cat_input = $this->input->post('cat');
            $add_catagory = "INSERT INTO catagory (`user_id_fk`,`cat_name`) VALUES ( '{$id}' ,'{$cat_input}' ) ";
            $result_catagory = $this->db->query($add_catagory);
            $retrive_catagory = "SELECT cat_id FROM catagory WHERE cat_name = '{$cat_input}' ";
            $result = $this->db->query($retrive_catagory)->row();
            $catagory_id = $result->cat_id; 
        }
        $articletext = $this->input->post('articletext',true);
        // echo $catagory_id; 
        // die();
        $sql = " INSERT INTO user_articles (`cat_id_fk`, `title`, `article`) VALUES ( '$catagory_id', '{$title}', '{$articletext}'); ";
        $result = $this->db->query($sql);
        $row = $this->db->affected_rows();
        if ($row) {
            return true;
        }
        else
        {
            echo "Couldn't perform query";
            die(mysqli_error($sql));
            return false;
        }
}

这是我的view_addaticle.php文件：

<div class="container">
<div class="row">
    <div class="col-xs-6">
        <?php
            // Display Result Using Ajax
            echo "<div id='result' style='display: none'>";
            echo "<div class='alert alert-success' role='alert'>Well done! You successfully read this important alert message....</div>";
            echo "</div>";
            echo "</div>";
        ?>
    </div>
    <div class="col-xs-6">
        <?php       
            echo validation_errors(); 
            echo form_open('article/submit_article'); #'add_post/submit_post'
        ?>
        <div class="form-group">
        <input type="hidden" name="hiddenValue" id="hiddenValue" value="<?php echo $session_data['id']; ?>">
            <label for="sel1">Title:</label>
                <input type="text" name="title" class="form-control" placeholder="Title of Article">
            <br>
            <!-- <label for="sel1">Select Catagory:</label> -->
          <script type="text/javascript">
                 function admSelectCheck(nameSelect)
            {
                 console.log(nameSelect);
                if(nameSelect){
                    admOptionValue = document.getElementById("admOption").value;
                    if(admOptionValue == nameSelect.value){
                        document.getElementById("admDivCheck").style.display = "block";
                    }
                    else{
                        document.getElementById("admDivCheck").style.display = "none";
                    }
                }
                else{
                    document.getElementById("admDivCheck").style.display = "none";
                }}
        </script> 

               <select name="catagory_select" class="selectpicker form-control" style=" width: 150px;" onchange='admSelectCheck(this);'> 
                <option>Select Catagory</option>  
                <?php
                    foreach ($query->result() as $key):
                ?>
                <option value="<?php echo $key->cat_id; ?>"><?php echo $key->cat_name; ?></option>
                <?php endforeach; ?>
                <option id="admOption">others</option>
              </select>
              <br>
              <div id="admDivCheck" style="display: none;">
                <input type="text" placeholder="Enter Catagory Name" class="form-control"  name="cat" id="color" style='width: 170px;'/>
                </div>
             <br>
            <label for="sel1">Article:</label>
            <textarea class="form-control" name="articletext" id="" cols="80" rows="10"></textarea>
            <br>
            <input class="btn btn-primary "  value="Submit Article" id="submit" type="submit" style="float:right;" />
            </div>
        </form>
    </div>
</div>

这是我的控制器函数submit_article（），位于article.php文件：中

public function submit_article()
{
    $this->form_validation->set_rules('title', 'Title', 'required');
    $this->form_validation->set_rules('articletext', 'Article Text', 'required');

    if ($this->form_validation->run() === FALSE)
    {
        $this->load->view('layouts/header');
        $this->load->view('view_addarticle');
        $this->load->view('layouts/footer');
    }
    else
    {
        $title = $this->input->post('title');
        $result = $this->model_article->add_article();
        if(!$result)
        {
            echo "Coulnd't register, contact site admin help@xyz.com";
        }
        else
        {
            // echo json_encode($result);
            redirect('account');
        }
    }
}