Linq查询操作符示例

    /// <summary>
    /// Select - Select选择；延迟
    /// </summary>
    private void Summary_Select()
    {
        var ary = _ctx.Categories.Select(
            c => new { CategoryName = "类别名称：" + c.CategoryName });

        foreach (var c in ary)
            result.InnerHtml += c.CategoryName + "<br />";

        var ary2 = from c in _ctx.Categories
                          select new { CategoryName = "类别名称：" + c.CategoryName };
        foreach (var c in ary2)
            result.InnerHtml += c.CategoryName + "<br />";

        result.InnerHtml += "<br />";
    }

    /// <summary>
    /// Where - Where查询；延迟
    /// </summary>
    private void Summary_Where()
    {
        var categories = _ary.Where(
            a => a.StartsWith("w") && a.EndsWith("f"));

        foreach (var a in categories)
            result.InnerHtml += a+"<br />";

        var categories2 = from a in _ary
                          where a.StartsWith("w") && a.EndsWith("f")
                          select a;
        foreach (var a in categories2)
            result.InnerHtml += a + "<br />";

        result.InnerHtml += "<br />";
    }

    /// <summary>
    /// OrderBy - 按指定表达式对集合正序排序；延迟
    /// OrderByDescending - 按指定表达式对集合倒序排序；延迟
    /// </summary>
    private void Summary_OrderByDescending()
    {
        var ary = (from a in _ary
                   select a).OrderByDescending(a => a.Length);
        foreach (var a in ary)
            result.InnerHtml += a + "<br />";

        var ary2 = from a in _ary
                   orderby a.Length descending
                   select a;
        foreach (var a in ary2)
            result.InnerHtml += a + "<br />";

        result.InnerHtml += "<br />";
    }

    /// <summary>
    /// GroupBy_OrderBy - 分组 + 排序；延迟
    /// </summary>
    private void Summary_GroupBy_OrderBy()
    {
        var list = (from a in _ary
                    select a).GroupBy(a => a.Length).Select(
                    g => new { Group = g.Key, Member = g }).OrderBy(a => a.Group);

        foreach (var g in list)
        {
            result.InnerHtml += g.Group + "个字符<br />" ;
            foreach (string m in g.Member)
                result.InnerHtml += "--" + m + "<br />";
            result.InnerHtml += "<br />";
        }

        var list2 = from a in _ary
                    group a by a.Length into g
                    orderby g.Key  
                    select new { Group = g.Key, Member = g };
        foreach (var g in list2)
        {
            result.InnerHtml += g.Group + "个字符<br />";
            foreach (string m in g.Member)
                result.InnerHtml += "--" + m + "<br />";
            result.InnerHtml += "<br />";
        }

        result.InnerHtml += "<br />";
    }

    /// <summary>
    /// Join - Join查询；延迟
    /// </summary>
    private void Summary_Join()
    {
        var products = _ctx.Products.Join(
            _ctx.Categories,
            p => p.CategoryID,
            c => c.CategoryID,
            (p, c) => new { c.CategoryName, p.ProductName }).Take(5);

        foreach (var p in products)
            result.InnerHtml +=p.CategoryName +"-"+p.ProductName+ "<br />";

        result.InnerHtml += "<br />";

        var products2 = (from p in _ctx.Products
                         join c in _ctx.Categories on p.CategoryID equals c.CategoryID
                         select new { c.CategoryName, p.ProductName }).Take(5);

        foreach (var p in products2)
            result.InnerHtml += p.CategoryName + "-" + p.ProductName + "<br />";

        result.InnerHtml += "<br />";
    }

    /// <summary>
    /// GroupJoin - 分组Join查询；延迟
    /// </summary>
    private void Summary_GroupJoin()
    {
        var categories = _ctx.Categories.GroupJoin(
            _ctx.Products,
            c => c.CategoryID,
            p => p.CategoryID,
            (c, g) => new { c.CategoryName, ProductCount = g.Count() });

        foreach (var c in categories)
            result.InnerHtml += c.CategoryName + "-" + c.ProductCount;
        result.InnerHtml += "<br />";

        var categories2 = from c in _ctx.Categories
                          join p in _ctx.Products on c.CategoryID equals p.CategoryID into g
                          select new { c.CategoryName, ProductCount = g.Count() };

        foreach (var c in categories2)
            result.InnerHtml += c.CategoryName + "-" + c.ProductCount;
        result.InnerHtml += "<br />";
    }

示例代码:https://files.cnblogs.com/hyosft/Linq%e6%9f%a5%e8%af%a2%e6%93%8d%e4%bd%9c%e7%ac%a6%e7%a4%ba%e4%be%8b.rar