我想在Entity Framework中过滤导航属性。从这里给出的例子https://docs.microsoft.com/en-us/ef/core/querying/related-data
import sys
import pygame as pg
from pygame.math import Vector2
width = 1280
height = 720
x1 = 200
y1 = 100
x2 = 500
y2 = 400
x3 = 100
y3 = 300
x = 0
y = 0
class Player(pg.sprite.Sprite):
def __init__(self, pos, *groups):
super().__init__(*groups)
pg.sprite.Sprite.__init__(self)
self.image = pg.image.load("character.png")
self.rect = self.image.get_rect(center=pos)
self.vel = Vector2(0, 0)
self.pos = Vector2(pos)
def update(self):
self.pos += self.vel
self.rect.center = self.pos
#enemy class
class Enemy(pg.sprite.Sprite):
def __init__(self, pos, waypoints, *groups):
super().__init__(*groups)
self.image = pg.image.load("enemy.png")
self.image = pg.transform.scale(self.image, (int(50), int(50)))
self.rect = self.image.get_rect(center=pos)
self.vel = Vector2(0,0)
self.max_speed = 5
self.pos = Vector2(pos)
self.waypoints = waypoints
self.waypoint_index = 0
self.target = self.waypoints[self.waypoint_index]
self.target_radius = 50
self.rect.x = width / 2
self.rect.y = height / 2
def update(self):
# A vector pointing from self to the target.
heading = self.target - self.pos
distance = heading.length() # Distance to the target.
heading.normalize_ip()
if distance <= 2: # We're closer than 2 pixels.
# Increment the waypoint index to swtich the target.
# The modulo sets the index back to 0 if it's equal to the length.
self.waypoint_index = (self.waypoint_index + 1) % len(self.waypoints)
self.target = self.waypoints[self.waypoint_index]
if distance <= self.target_radius:
# If we're approaching the target, we slow down.
self.vel = heading
else: # Otherwise move with max_speed.
self.vel = heading * self.max_speed
self.pos += self.vel
self.rect.center = self.pos
#Enemy waypoints
waypoints = [[x1, y1], [x2, y2], [x3, y3]]
class Floor(pg.sprite.Sprite):
def __init__(self, x, y, *groups):
super().__init__(*groups)
self.image = pg.image.load("floor.png")
self.rect = self.image.get_rect(topleft=(x, y))
self.rect.x = x
self.rect.y = y
class SideWall(pg.sprite.Sprite):
def __init__(self, x, y, *groups):
super().__init__(*groups)
self.image = pg.image.load("sidewall.png")
self.rect = self.image.get_rect(topleft=(x, y))
self.rect.x = x
self.rect.y = y
class TopAndBottomWall(pg.sprite.Sprite):
def __init__(self, x, y, *groups):
super().__init__(*groups)
self.image = pg.image.load("topandbottomwall.png")
self.rect = self.image.get_rect(topleft=(x, y))
self.rect.x = x
self.rect.y = y
def main():
screen = pg.display.set_mode((1280, 720))
clock = pg.time.Clock()
#all the sprites group
all_sprites = pg.sprite.Group()
#the floor
floor = Floor(540, -620, all_sprites)
#player
player = Player(((width / 2), (height / 2)), all_sprites)
#walls group
walls = pg.sprite.Group()
#all walls
walltop = TopAndBottomWall(540, -620, all_sprites, walls)
wallbottom = TopAndBottomWall(540, 410, all_sprites, walls)
wallleft = SideWall((width / 2) - 100, (height / 2) - 930, all_sprites, walls)
wallright = SideWall((wallleft.rect.x + (1920 - 50)), (height / 2) - 930, all_sprites, walls)
#all enemy's
enemy = Enemy((100, 300), waypoints, all_sprites)
camera = Vector2(0, 0)
done = False
while not done:
for event in pg.event.get():
if event.type == pg.QUIT:
done = True
#player movement
elif event.type == pg.KEYDOWN:
if event.key == pg.K_d:
player.vel.x = 5
elif event.key == pg.K_a:
player.vel.x = -5
elif event.key == pg.K_w:
player.vel.y = -5
elif event.key == pg.K_s:
player.vel.y = 5
elif event.type == pg.KEYUP:
if event.key == pg.K_d and player.vel.x > 0:
player.vel.x = 0
elif event.key == pg.K_a and player.vel.x < 0:
player.vel.x = 0
elif event.key == pg.K_w:
player.vel.y = 0
elif event.key == pg.K_s:
player.vel.y = 0
camera -= player.vel
all_sprites.update()
if pg.sprite.spritecollide(player, walls, False):
#stop the left wall from moving
wallleft.rect.x = wallleft.rect.x + player.vel.x
wallleft.rect.y = wallleft.rect.y + player.vel.y
#stop the top wall from moving
walltop.rect.y = walltop.rect.y + player.vel.y
walltop.rect.x = walltop.rect.x + player.vel.x
#stop the right wall from moving
wallright.rect.x = wallright.rect.x + player.vel.x
wallright.rect.y = wallright.rect.y + player.vel.y
#stop the bottom wall from moving
wallbottom.rect.x = wallbottom.rect.x + player.vel.x
wallbottom.rect.y = wallbottom.rect.y + player.vel.y
#stop the floor from moving
floor.rect.x = floor.rect.x + player.vel.x
floor.rect.y = floor.rect.y + player.vel.y
screen.fill((0, 0, 0))
for sprite in all_sprites:
screen.blit(sprite.image, sprite.rect.topleft+camera)
pg.display.flip()
clock.tick(30)
main()
pg.quit()
如果我想过滤特定博客和特定帖子，我该如何过滤？即使帖子不存在，也必须返回博客详细信息
我想要一些像下面的东西
using (var context = new BloggingContext())
{
var blogs = context.Blogs
.Include(blog => blog.Posts)
.ToList();
}
在上述情况下，如果postid 2可用于blogid 1则应返回两者。如果博客可用，则应仅返回博客详细信息。我怎样才能做到这一点？
从SQL的角度来看，它就像一个左连接。
此致 乔
答案 0 :(得分：0)
两个查询的群组联接应该有效（以下假设您希望每个博客发布一个帖子，如果不是这样，请删除FirstOrDefault（））：
var blogs = context.Blogs.Where(a => a.BlogId == 1);
var posts = context.Posts.Where(a => a.PostId == 2);
var blogWithPost = blogs.GroupJoin(posts, a => a.BlogId, a => a.PostId, (a,b) => new { Blog=a, Post = b.FirstOrDefault() });