Mine are in containers too, and I drag them to an area where they get sunlight through the trees. Even if it's still too hot to set fruit, it gives them a break so they're less stressed when it cools off enough. Seems to work for me. One reason I like containers, so I can do just this.

In some drought years when I have grown tomato plants in containers, I have moved them into more shade as the heat gets worse. It doesn't hurt them much since they already aren't setting fruit, but it could slow down the maturing of any fruit that already has set, so keep that in mind. I try to ensure my shaded ones get at least 4-6 hours of sunlight even in the worst heat, but if you can't do that, just do the best you can.

Even with plants in the ground, you can shade them to help get them through the worst heat. I use a 50% shade cloth (it blocks 50% of the light) over them, suspended on PVC pipes roughly a foot above the plants to allow for good air flow between the top of the plants and the bottom of the shade cloth in order to prevent the plants from roasting to death. I generally don't shade them until we're going over 100 degrees daily, so often not until sometime in July, but you can shade them as you see fit. I get pretty good fruit set from tomato plants at the west end of the garden where they get direct sunlight from sunrise until about noon and then fairly heavy shade for the rest of the day. For tomato plants to be in full direct sunlight from sunrise to sunset here in OK is actually pretty brutal for the plants in the summer months.