Is a contract that allows only one party to collect attorney fees enforceable?

Civil Code section 1717, subdivision (a) provides that "[i]n any action on a contract, where the contract specifically provides that attorney's fees and costs, which are incurred to enforce that contract, shall be awarded either to one of the parties or to the prevailing party, then the party who is determined to be the party prevailing on the contract, whether he or she is the party specified in the contract or not, shall be entitled to reasonable attorney's fees in addition to other costs." In other words, contractual attorney fees are reciprocal: Even if a contract by its own terms allows only one party to obtain attorney fees, under section 1717, the other party is eligible for attorney fees if it prevails. (Santisas v. Goodin (1998) 17 Cal.4th 599, 610-611.) In addition, if a party sues under a contract that would allow it to collect attorney fees, and the opposing party successfully demonstrates that the contract is invalid, the prevailing party is still entitled to contractual attorney fees under section 1717. (Santisas v. Goodin, supra, at p. 611.)