title: SQLAlchemy: Check if object is already present in table
body: <p>I have a class <code>Item</code> whose <code>id</code> is a primary key and auto-generated. Now I read data from some other external source, create an <code>Item</code> object, and need to check if this object is already present in my <code>items</code> table. How do I do it?</p>