SqlSugar常用查询实例-拉姆达表达式

SqlSugar支持拉姆达表达式查询，匿名对象参数等，相对还是比较方便好用的。

一.查询列表：

    //查询列表
    SqlSugarClient db = SugarContext.GetInstance();
    List tList = db.Queryable().ToList();
    Console.WriteLine(tList.Count);

    var studentDynamic = db.Queryable().ToDynamic();
    Console.WriteLine(studentDynamic);

    string teaJson = db.Queryable().ToJson();
    Console.WriteLine(teaJson);

    //Json序列化的DateTime处理 
    db.SerializerDateFormat = "yyyy年MM月dd日";
    string teacher1 = db.Queryable().OrderBy("tbirthday desc").Take(2).ToJson();
    string teacher2 = db.Sqlable().From("t").SelectToJson(" top 1 *");
    string teacher3 = db.SqlQueryJson("select top 1 * from teacher;");
    Console.WriteLine(teacher1);
    Console.WriteLine(teacher2);
    Console.WriteLine(teacher3);
    Console.WriteLine(tList.First().tbirthday.Value.ToString("yyyy-MM-dd"));

特别说明：

1、SqlSugar类库中的json序列化使用的.Net自带的“JavaScriptSerializer”

2、其中Date的格式化原理是先生成json，字符串/\/Date(xxxx)\/，将取出总毫秒数再进行转换。更多点击参考

3.源代码中的日期转化不支持1970年以前的时间，但是可以自己修改一下：

           // string pattern = @"\\/Date\((\d+)\)\\/"; //源代码中的正则
            string pattern = @"\\/Date\((-*\d+)\)\\/"; //2016-11-22 修改正则

二、常用查询

//查询单条
SqlSugarClient db = SugarContext.GetInstance();
teacher tea1 = db.Queryable().Single(t => t.tno == "804");//如果查询数据库没有数据，抛出异常
Console.WriteLine(tea1.tname);
//根据主键查询单条
teacher tea2 = db.Queryable().InSingle("814");//如果查询数据为空，返回null
Console.WriteLine(tea2.ToJsonString());// 输出：null
/***考虑查询为空的情况***/
teacher tea3 = db.Queryable().SingleOrDefault(t => t.tno == "814");
Console.WriteLine(tea3.ToJsonString());// 输出：null
teacher tea4 = db.Queryable()
    .Where(q => q.tno == "814")
    .FirstOrDefault(); //此处扩展方法仿EF First()/FirstOrDefault()
Console.WriteLine(tea4.ToJsonString()); // 输出：null


/*****常用查询******/
//1.判断是否存在
bool exists1 = db.Queryable().Any(q => q.tno == "814");
Console.WriteLine(exists1);
//2.模糊查询，含有
List contains1 = db.Queryable()
    .Where(q => q.tname.Contains("李"))
    .ToList();
Console.WriteLine(contains1.ToJsonString());
//以xxx结尾
List end1 = db.Queryable()
        .Where(q => q.tname.EndsWith("成"))
        .ToList();
Console.WriteLine(end1.ToJsonString());
//3. in关键词查询
string[] idList = new string[] { "804", "825" };
List in1 = db.Queryable()
    .In(q => q.tno, idList)  //如果不支持拉姆达表达式，默认为主键
    .ToList();
Console.WriteLine(in1.ToJsonString());
List in2 = db.Queryable()
    .Where(q => idList.Contains(q.tno))
    .ToList();
Console.WriteLine(in2.ToJsonString());


/*********汇总查询等***********/
//1.获取总数
int count = db.Queryable()
    .Where(q => q.tsex == "男")
    .Count();
Console.WriteLine("count=" + count);
//2.获取最大值
decimal maxDegree = db.Queryable()
    .Where(q => q.cno == "3-105")
    .Max(q => q.degree) //此处Max返回的结果为Object需要拆箱
    .ObjToDecimal();
Console.WriteLine("maxDegree:" + maxDegree);
//3.获取最小值
decimal minDegree = db.Queryable()
    .Where(q => q.cno == "3-105")
    .Min(q => q.degree)
    .ObjToDecimal();
Console.WriteLine("minDegree:" + minDegree);
//4.平均值
//SqlSugar 不支持 平均值的扩展方法

/***复杂的查询可以使用Sql字符串实现***/
//var list = db.Queryable().Where("id=@id and name=@name", new { id = 1, name = xxx }).ToList();

三、分页查询：

//分页查询处理
SqlSugarClient db = SugarContext.GetInstance();
//分页方式1
Queryable query = db.Queryable();
query = query.Where(q => q.tno.StartsWith("8"));
//排序
//query = query.OrderBy("tbirthday desc"); //排序说明，如果是倒叙，需要传入排序的sql片段
query = query.OrderBy(q => q.tbirthday);    //如果是正序，可以指定拉姆达表达式
int allCount = query.Count();
//分页
//List list1 = query.Skip(1).Take(2).ToList();
//或者
List list1 = query.ToPageList(1, 2);
Console.WriteLine("list1-count:" + allCount);
Console.WriteLine("list1:" + list1.ToJsonString());


//分页方式2+符合查询 多where是and拼接
Queryable query2 = db.Queryable();
query2 = query2.Where(q => q.ssex == "男");
query2 = query2.Where(q => q.sname.EndsWith("军"));
//排序
query2 = query2.OrderBy(q => q.sbirthday);
int allCount2 = 0;
//分页
List list2 = query2.ToPageList(1, 2, ref allCount2);
Console.WriteLine("list2-count:" + allCount2);
Console.WriteLine("list2:" + list2.ToJsonString());

四、汇总查询2

//分组，查询汇总
SqlSugarClient db = SugarContext.GetInstance();
dynamic result1 = db.Queryable()
    .GroupBy(q => q.ssex)
    .Select("ssex,count(*) Count")
    .ToDynamic();
foreach (var item in result1)
{
    Console.WriteLine(item.ssex + "----" + item.Count);
}

string result2 = db.Queryable()
    .GroupBy(q => q.sno)
    .Select("sno,isnull(sum(degree),0)")
    .ToJson();
Console.WriteLine(result2);

五、关联表查询

static void QueryFive()
{
    //关联表查询，筛选等
    SqlSugarClient db = SugarContext.GetInstance();
    //将结果转换成其他对象
    var result = db.Queryable()
        .JoinTable((s1, s2) => s1.sno == s2.sno)
        .OrderBy(s1 => s1.degree)
        .Take(1)
        .Select((s1, s2) => new Score_Student
        {
            sno = s1.sno,
            sname = s2.sname,
            cno = s1.cno,
            degree = s1.degree
        }).ToList();
    Console.WriteLine(result.ToJsonString());
    //输出结果
    //[{"sno":"101","sname":"李军","degree":64.0,"cno":"3-105"}]

    //关联查询
    //特别说明：如果指定了关联表代表参数s1,s2,那么在后边的筛选等操作中需要使用表字段的地方，必须使用s1或s2
    var result2 = db.Queryable()
        .JoinTable((s1, s2) => s1.sno == s2.sno)
        .Where(s1 => s1.degree > 64)
        .Where(s1 => s1.degree < 70)
        .ToJson();
    Console.WriteLine(result2);
    //输出结果：
    //[{"sno":"109","cno":"3-245","degree":68.0,
    //"sno1":"109","sname":"王芳","ssex":"女","sbirthday":"\/Date(161193600000)\/","class":"95031"}]


    //获取单个表的投影
    //特别说明，如果想获取单个表的投影，需要先将查询结果.ToList(),然后在创建匿名对象
    //或者 Select()中使用sql指定列名
    var result3 = db.Queryable()
        .OrderBy(q => q.sbirthday)
        .Take(1)
        .ToList()
        .Select(q => new
        {
            sno = q.sno,
            sname = q.sname
        });
    Console.WriteLine(result3.ToJsonString());
    //输出结果：
    //[{"sno":"103","sname":"陆军"}]


    //获取多个表，投影
    var result4 = db.Queryable()
        .JoinTable((s1, s2) => s1.sno == s2.sno)
        .OrderBy(s1 => s1.degree)
        .Take(1)
        .Select("s1.*,s2.sname as sname")
        .ToJson();
    Console.WriteLine(result4);
    //输出结果：
    //[{"sno":"101","cno":"3-105","degree":64.0,"sname":"李军","row_index":1}]
}
public class Score_Student
{
    public string sno { get; set; }
    public string sname { get; set; }
    public decimal degree { get; set; }
    public string cno { get; set; }
}

更多参考：

.Net开源SqlServer ORM框架SqlSugar整理

SqlSugar框架T4模板的使用