efcore 预先加载和显示加载的使用

官网: https://learn.microsoft.com/zh-cn/ef/core/querying/related-data/eager
预先加载的使用: 

关联两张表查询

using (var context = new BloggingContext())
{var blogs = context.Blogs.Include(blog => blog.Posts).Include(blog => blog.Owner).ToList();
}

查询多层级关联

using (var context = new BloggingContext())
{var blogs = context.Blogs.Include(blog => blog.Posts).ThenInclude(post => post.Author).ThenInclude(author => author.Photo).ToList();
}

显示加载的使用: 
DbContext.Entry(...) API 显式加载导航属性。

显示加载导航属性

using (var context = new BloggingContext())
{var blog = await context.Blogs.SingleAsync(b => b.BlogId == 1);await context.Entry(blog).Collection(b => b.Posts).LoadAsync();await context.Entry(blog).Reference(b => b.Owner).LoadAsync();
}

 

显示查询多层级关联

using (var context = new BloggingContext())
{var blog = await context.Blogs.SingleAsync(b => b.BlogId == 1);
await context.Entry(blog).Collection(b => b.Posts)
　　　　　.Query()
　　　　　.Include(r => r.Books)
　　　　　.LoadAsync()

}

 

显示查询关联实体

using (var context = new BloggingContext())
{var blog = await context.Blogs.SingleAsync(b => b.BlogId == 1);var postCount = await context.Entry(blog).Collection(b => b.Posts).Query().CountAsync();
}

 

筛选要加载到内存中的关联实体

using (var context = new BloggingContext())
{var blog = await context.Blogs.SingleAsync(b => b.BlogId == 1);var goodPosts = await context.Entry(blog).Collection(b => b.Posts).Query().Where(p => p.Rating > 3).ToListAsync();
}