I know that bitcoin blocks are going to be halved to 12.5 next summer.
so how will this affect the price?
I don't think it really will effect the price very much. Everyone knows it is going to happen, and have known for years. Just like we know approximately when it will halve again.
halving will certainly effect bitcoin price not due to people holding hoping for price rise after halving but due to holding of coin by miners to sell high to recover their cost on mining it.