title: Why doesn't save() work in Sequelize?
body: <p>I call <code>save()</code> on an object that already exists in my database and has a primary key defined.</p>
  
  <p>Instead of updating the object, Sequelize tells me <code>id must be unique</code>. Why?</p>
  
  <p>I don't want to have to say <code>update( {every,single,field,except,the,id})</code>. That's so tedious.</p>
  
  <p>Here's my current code:</p>
  
  <pre><code>const instance = db.dbo__peach_payments_transactions.build(existingPayment);
  return db.transaction( async (transaction) =&gt; {
    return instance.save();
  });
  </code></pre>
  
  <hr>
  
  <p>I've also now tried:</p>
  
  <pre><code>return instance.update({fields: [
            'updated_at',
            'orders_id',
            'payment_states_id',
            'response_data',
            'token',
            'result',
            'reason_code',
            'reason_message',
            'price',
            'processed_at']});
        });
  </code></pre>
  
  <p>but this generates the <strong>opposite</strong> sql, instead of saving those fields, it excludes them giving me the error: <code>updated_at cannot be null</code> (even when it's not null) with this sql:</p>
  
  <p><code>"INSERT INTO "dbo"."peach_payments_transactions" ("peach_payments_transactions_id","created_at") VALUES ('7fb301e9-bb72-4a70-9ee5-0db1376e83e8','2016-07-11 13:48:20.137 +00:00') RETURNING *;"</code></p>