Php _ troubleshooting _ sessioin

Php _ error solving _ problems encountered when writing to the shopping cart by sessioin ,?? Fatalerror: DangdangService: addCartItem () [& lt; ahref = 'dangdangservice. addcartitem '& gt; dangdangservice. php _ sessioin

An error occurred while writing the shopping cart,

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Fatal error: DangdangService: addCartItem () [dangdangservice. addcartitem]: The script tried to execute a method or access a property of an incomplete object. please ensure that the class definition "Cart" of the object you are trying to operate on was loaded _ before _ unserialize () gets called or provide a _ autoload () function to load the class definition

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Query discovery;

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$ Car = null;
If (empty ($ _ SESSION ['car']) {
?? $ Uid = $ _ SESSION ['uid']; ???
?? $ Car = DangdangService: getInstance ()-> createCart ($ uid, $ bookId );
?? // Php features, objects, stored in session, serialized
?? $ _ SESSION ['car'] = serialize ($ car );
?? // $ _ SESSION ['cart'] = $ car;
} Else {
??? $ Car = unserialize ($ _ SESSION ['card']);
??? // $ Car = $ _ SESSION ['car'];
??? $ _ SESSION ['car'] = serialize (DangdangService: getInstance ()-> addCartItem ($ car, $ bookId ));
??? // $ _ SESSION ['car'] = DangdangService: getInstance ()-> addCartItem ($ car, $ bookId );
}
$ OSmarty-> assign ("items", $ car-> getItems ());
$ OSmarty-> display ("car.html ");

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Is php serialized when accessing objects in a session? :)