LINQ 查询

LINQ 查询

Entity Framework Core 使用语言集成查询（LINQ）来查询数据库中的数据。

加载所有数据

using (var context = new BloggingContext())
{
    var blogs = context.Blogs.ToList();
}Code language: JavaScript (javascript)

加载单个实体

using (var context = new BloggingContext())
{
    var blog = context.Blogs
        .Single(b => b.BlogId == 1);
}Code language: JavaScript (javascript)

筛选

using (var context = new BloggingContext())
{
    var blogs = context.Blogs
        .Where(b => b.Url.Contains("dotnet"))
        .ToList();
}Code language: JavaScript (javascript)

投影转换

var blogs = context.Blogs
    .OrderByDescending(blog => blog.Rating)
    .Select(blog => new
    {
        Id = blog.BlogId,
        Url = StandardizeUrl(blog.Url)
    })
    .ToList();

public static string StandardizeUrl(string url)
{
    url = url.ToLower();

    if (!url.StartsWith("http://"))
    {
        url = string.Concat("http://", url);
    }

    return url;
}Code language: JavaScript (javascript)