我有三个表，名称++，-- Copyright © 2017 Martin Ueding <dev@martin-ueding.de>
-- Ising model with the Metropolis algorithm. Random choice of lattice site for
-- a spin flip.
import qualified Data.Text
import System.Random
type Spin = Bool
type Lattice = [Spin]
-- Lattice extent is fixed to a square.
extent = 30
volume = extent * extent
temperature :: Double
temperature = 0.0
-- Converts a `Spin` into `+1` or `-1`.
spin :: Spin -> Int
spin True = 1
spin False = (-1)
-- Wrap a coordinate for periodic boundary conditions.
wrap :: Int -> Int
wrap = flip mod $ extent
-- Converts an unbounded (x,y) index into a linearized index with periodic
-- boundary conditions.
index :: Int -> Int -> Int
index x y = wrap x + wrap y * extent
-- Retrieve a single element from the lattice, automatically performing
-- periodic boundary conditions.
get :: Lattice -> Int -> Int -> Spin
get l x y = l !! index x y
-- Computes the sum of neighboring spings.
neighborSum :: Lattice -> Int -> Int -> Int
neighborSum l x y = sum $ map spin $ map retriever neighbors
where
retriever = \(x, y) -> get l x y
neighbors = [(x+1,y), (x-1,y), (x,y+1), (x,y-1)]
-- Computes the energy difference at a certain lattice site if it would be
-- flipped.
energy :: Lattice -> Int -> Int -> Int
energy l x y = 2 * neighborSum l x y * (spin (get l x y))
-- Converts a full lattice into a textual representation.
latticeToString l = unlines lines
where
spinToChar :: Spin -> String
spinToChar True = "#"
spinToChar False = "."
line :: String
line = concat $ map spinToChar l
lines :: [String]
lines = map Data.Text.unpack $ Data.Text.chunksOf extent $ Data.Text.pack line
-- Populates a lattice given a random seed.
initLattice :: Int -> (Lattice,StdGen)
initLattice s = (l,rng)
where
rng = mkStdGen s
allRandom :: Lattice
allRandom = randoms rng
l = take volume allRandom
-- Performs a single Metropolis update at the given lattice site.
update (l,rng) x y
| doUpdate = (l',rng')
| otherwise = (l,rng')
where
shift = energy l x y
r :: Double
(r,rng') = random rng
doUpdate :: Bool
doUpdate = (shift < 0) || (exp (- fromIntegral shift / temperature) > r)
i = index x y
(a,b) = splitAt i l
l' = a ++ [not $ head b] ++ tail b
-- A full sweep through the lattice.
doSweep (l,rng) = doSweep' (l,rng) (extent * extent)
-- Implementation that does the needed number of sweeps at a random lattice
-- site.
doSweep' (l,rng) 0 = (l,rng)
doSweep' (l,rng) i = doSweep' (update (l,rng'') x y) (i - 1)
where
x :: Int
(x,rng') = random rng
y :: Int
(y,rng'') = random rng'
-- Creates an IO action that prints the lattice to the screen.
printLattice :: (Lattice,StdGen) -> IO ()
printLattice (l,rng) = do
putStrLn ""
putStr $ latticeToString l
dummy :: (Lattice,StdGen) -> IO ()
dummy (l,rng) = do
putStr "."
-- Creates a random lattice and performs five sweeps.
main = do
let lrngs = iterate doSweep $ initLattice 2
mapM_ dummy $ take 1000 lrngs
，A：
B我想获得波纹管数据：
C你看，有三级数据，如果只有表A和B，我可以多表连接查询：
class A(models.Model):
name = models.CharField(max_length=12)
class B(models.Model):
name = models.CharField(max_length=12)
a = models.ForeignKey(to=A)
class C(models.Model):
name = models.CharField(max_length=12)
email = models.EmailField()
b = models.ForeignKey(to=B)
但是现在有三个表，您看到表[
{"name":"a1",
"data":[{
"name":"b1",
"data":[
{"name":"c1",
"data":{"c1_name":"c1_name", "c1_id":"c1_id"}
},
{"name":"c2",
"data":{"c2_name":"c2_name", "c2_id":"c2_id"}
}
]
},
{
"name":"b2",
"data":[
{"name":"c1",
"data":{"c1_name":"c1_name", "c1_id":"c1_id"}
},
{"name":"c2",
"data":{"c2_name":"c2_name", "c2_id":"c2_id"}
}
]
}
]
}
]
的电子邮件不包含在查询数据中。
如何在我的场景中实现这个要求？
答案 0 :(得分：0)
正如@Brian H.在评论中指出的那样，你可以用[{1}}链接外键。
在您的情况下，您可以使用
获取数据__然后，您可以循环访问数据并以您需要的格式构建列表。