Codeigniter：活动记录插入唯一值

I am importing GMail contacts from Google API and just want to persist unique email ids into database. Is it possible to insert unique records using codeigniter's Active Record? Does CodeIgniter provide it out of the box?
If I make the column unique the query throws exception. After digging into documentation I understood that CodeIgniter doesn't provide try catch blocks.

You can create a base model (application/core/MY_Model.php) and implement a save function to insert if new and update if exists. Extend your model from it.

This is an extract from http://thephpcode.com/blog/codeigniter/a-smart-codeigniter-model

public function save($data,$tablename="")
{
if($tablename=="")
{
    $tablename = $this->table;
}
$op = 'update';
$keyExists = FALSE;
$fields = $this->db->field_data($tablename);
foreach ($fields as $field)
{
    if($field->primary_key==1)
    {
        $keyExists = TRUE;
        if(isset($data[$field->name]))
        {
            $this->db->where($field->name, $data[$field->name]);
        }
        else
        {
            $op = 'insert';
        }
    }
}

if($keyExists && $op=='update')
{
    $this->db->set($data);
    $this->db->update($tablename);
    if($this->db->affected_rows()==1)
    {
        return $this->db->affected_rows();
    }
}

$this->db->insert($tablename,$data);

return $this->db->affected_rows();

}

If your data comes from a from, CI provides a form_validation class that can validate your form on the server side.By form_validation has a rule called is_unique its checks if the given value is already exist on the database or not. you can see a complete and clear explanation here

Or, you can check it manually before inserting your email in that unqiue column.

$this->db->select('email');
$this->db->where(array('email'=>$email));
$query = $this->db->get('yourtable');
if($query->num_rows() > 0){
    // the query returned data, so the email already exist.
}else{
    // the email not exists, so you can insert it.
}

your email field have to be unique in your table indexes.

$query_string = $this->db->insert_string('table', $data);
$query_string = str_replace('INSERT INTO', 'INSERT IGNORE INTO', $query_string);

$req = $this->db->query($query_string);

if($req->affected_rows() == 1) {
   //data inserted
} else {
   //email exists already
}

If you use the IGNORE keyword, errors that occur while executing the INSERT statement are treated as warnings instead. For example, without IGNORE, a row that duplicates an existing UNIQUE index or PRIMARY KEY value in the table causes a duplicate-key error and the statement is aborted. With IGNORE, the row still is not inserted, but no error is issued. Data conversions that would trigger errors abort the statement if IGNORE is not specified. With IGNORE, invalid values are adjusted to the closest values and inserted; warnings are produced but the statement does not abort.

MySQL INSERT syntax

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