Does logic board A1278 of MBP Unibody 2012 compatible with MBP 2009?

The parts you need (RAM, motherboard, heatsink and hard drive cable) will likely be as much as a 2012 with cosmetic damage warranting a discount that can be hidden with a case or left alone and used as you got it. You can generally snag these at a pretty good discount (depending on the damage), especially if the seller can’t move it when you buy it. I got my 2011 for sub $200 over 2 minor dents and minor LCD assembly scratching that's acceptable. There is a pressure mark on the LCD, but I hid that with a very similar background and you can’t tell easily with the backlit dimmed (which I’d do anyway to save power). The catch is I had to buy a genuine charger because eBay sellers have a love affair with fakes which are considered a "high grade copy" as a cautionary step. This negated my savings a little bit, but not too much. I still came out ahead despite needing to dump the seller’s MagSafe. This is how bad they are now, and why I’m at a point I tell eBay buyers to protect the machine before it shows up and get a real adapter before the computer arrives:

The holes on the boards look like they line up as well so that isn’t an issue. The RAM your 2009 came with won’t work since it is 1066MHz and the newer machines ship with 1333 (2011) or 1600 (2012). In theory the 2011 should accept 1600MHz RAM and downclock it, which will be the way to go since 1333 is rare and expensive. If you can’t find cheap 1333MHz RAM, 1600MHz will downclock and run at the 1333MHz speed on a 2011.

In addition to all of those incompatibilities, the display and AirPort card (including the mount) need to be replaced. The 2009 display doesn't carry over to the older systems due to the wireless antenna configuration being completely different between the two. Retrofitting 2011 parts is about as much as the assembly as well, so it doesn’t make sense to refurb the 2009 part to work on a 2011.

If you are strapped for cash, you are probably better off with a discounted 2012 that works but has worse than average cosmetics. These tend to need a few things addressed, but nowhere near as many as a model conversion like you want to do. This is what a 2011/12 needs:

• Hard drive cable (with protective patching) (Some 2012’s are not affected; check the model of drive it came with if Apple OEM)
  • This needs to be addressed on ALL 2011’s without it done (some are, but not all). 2012 needs a visual check and potentially have it addressed on early ones. The early cables don’t work with modern SATA III drives.
  • Check the OEM drive specs if wasn’t replaced to see if it’s a SATA III part or not to get a clue on if the 2012 needs the fix.
  • If you have a working 2011 cable and it works in some capacity, use that luck to address it before it fails. Most of them look okay but are degraded internally.
• Thermal paste (2011/12)
  • Most of these have dead end thermal paste as it never seems to be done. Do it yourself and be sure.
• Battery (2011/12)
  • Most of these have a lot of cycles at this point. Expect it to need to be addressed under your use.

This is the *bad* cable:

In addition, many of these machines come with the old cable and are not SATA III rated, which results in drive compatibility issues. In addition to that problem, you probably need to repaste the CPU and clean out the dust to be sure it is done. The case feet also have a habit of failing, so you may want to buy a set to have on hand for when it inevitably happens - if it hasn’t already happened because you moved it when it was their time to fail. Inspect the feet while you’re there and look at replacing them so you will never have to worry about it.