参考地址：https://www.cnblogs.com/lunawzh/p/6607116.html
1、连接语句
var conn = new SqlConnection(ConfigurationManager.ConnectionStrings["SqlDiagnosticsDb"].ConnectionString);
使用dapper不需要考虑conn是否连接，在执行dapper时自行判断 open状态，如果没有打开它会自己打开。
2、insert
string query = "INSERT INTO Book(Name)VALUES(@name)"; conn.Execute(query, book);
book类中有name属性，就可以这样方便去写，当然也可以写成
string query = "INSERT INTO Book(Name)VALUES(@name)";
conn.Execute(query, new{@name=book.name});
3、update
string query = "UPDATE Book SET Name=@name WHERE id =@id"; conn.Execute(query, book);
4、 delete
string query = "DELETE FROM Book WHERE id = @id";
conn.Execute(query, book);
conn.Execute(query, new { id = id });
5、query
string query = "SELECT * FROM Book";
//无参数查询，返回列表，带参数查询和之前的参数赋值法相同。
conn.Query<Book>(query).ToList();
//返回单条信息
string query = "SELECT * FROM Book WHERE id = @id";
book = conn.Query<Book>(query, new { id = id }).SingleOrDefault();
6、 传统sql in (1,2,3) 用dapper就这样写
conn.Query<Users>("SELECT * FROM Users s WHERE s.id IN (@ids) ",new { ids = new int[]{1,2,3}})
conn.Query<Users>("SELECT * FROM Users s WHERE s.id IN (@ids) ",new { ids = IDs.ToArray()})
在dapper因为安全性，不能直接用sql接接 要采用参数化,
7、批量插入
conn.Execute(@"insert MyTable(colA, colB) values (@a, @b)", new[] { new { a=1, b=1 }, new { a=2, b=2 }, new { a=3, b=3 } })
也可以直接写入一个集合
conn.Execute("insert user(name) values(@name)",users)
这里users是一个user表的对象集合，可一次把集合中的所有数据插入到数据表中。
8、多表查询
//查询图书时，同时查找对应的书评，并存在List中。实现1--n的查询操作
string query = "SELECT * FROM Book b LEFT JOIN BookReview br ON br.BookId = b.Id WHERE b.id = @id";
Book lookup = null;
//Query<TFirst, TSecond, TReturn>
var b = conn.Query<Book, BookReview, Book>(query,
(book, bookReview) =>
{
//扫描第一条记录，判断非空和非重复
if (lookup == null || lookup.Id != book.Id)
lookup = book;
//书对应的书评非空，加入当前书的书评List中，最后把重复的书去掉。
if (bookReview != null)
lookup.Reviews.Add(bookReview);
return lookup;
}, new { id = id }).Distinct().SingleOrDefault();
return b;
多表联合查询是比较麻烦一些，到现在不是完全明白，多看几个例子
var sql = @"select * from Posts p join Users u on u.Id = p.OwnerId Order by p.Id";
var data = conn.Query<Post, User, Post>(sql, (post, user) => { post.Owner = user; return post;}，splitOn："id");
Post类和User类,它们存在外键， conn.Query返回的类型是最后一个参数Post, 其中Post中有一属性Owner是User对象，在(post, user)=>lamda中指定了Owner值，上边的代码中的splitOn是ID，运行时，会从查询结果所有字段列表的最后一个字段开始进行匹配，一直到找到Id这个字段（大小写忽略），找到的第一个ID字段匹配User类的ID属性，那么从ID到最后一个字段都属于User，ID以前的字段都被影射到Post， 通过 (post, user) => { return post;},把两个类的实例解析出来。
9、三表查询，一个是关联主键表（单个对象），一个是关联外键表（集合）。
public partial class UserInfo
{
public UserInfo()
{
this.Persion = new HashSet<Persion>();
this.MyTYC = new HashSet<MyTYC>();
}
public int id { get; set; }
public string name { get; set; }
public Nullable<System.DateTime> createTime { get; set; }
public Movies Movies { get; set; }
public virtual ICollection<MyTYC> MyTYC { get; set; }
}
public class Movies
{
public int ID { get; set; }
public string Title { get; set; }
public string ReleaseDate { get; set; }
public string Genre { get; set; }
public string Price { get; set; }
public UserInfo UserInfo { get; set; }
}
public partial class MyTYC
{
public int id { get; set; }
public string name { get; set; }
}
string sql = @"select * from UserInfo u
inner join [Movies].dbo.Movies m on u.id=m.ID
inner join MyTYC t on u.id=t.id";
var data = conn.Query<UserInfo, Movies, MyTYC, UserInfo>(sql, (u, m, t) => { u.Movies = m; u.MyTYC.Add(t); return u; });
注意这里的对象和集合的获取方法：u.Movies = m; u.MyTYC.Add(t);
10、多结果查询
var sql = @"select * from Customers where CustomerId = @id;
select * from Orders where CustomerId = @id;
select * from Returns where CustomerId = @id";
using (var multi = connection.QueryMultiple(sql, new {id=selectedId}))
{
var customer = multi.Read<Customer>().Single();
var orders = multi.Read<Order>().ToList();
var returns = multi.Read<Return>().ToList();
}
再来一个
class Program
{
//创建连接对象
protected static SqlConnection GetConnection()
{
var connection = new SqlConnection("Data Source=.;Initial Catalog=TestDB;Integrated Security=True");
connection.Open();
return connection;
}
static void Main(string[] args)
{
//测试输出多个结果集
var sql = @"INSERT INTO [dbo].[Student] ([Name]) VALUES ('A1'); select @@IDENTITY as A;
INSERT INTO [dbo].[Student] ([Name]) VALUES ('B1'); select @@IDENTITY as A;
INSERT INTO [dbo].[Student] ([Name]) VALUES ('C1'); select @@IDENTITY as A";
//初始化数据库连接
using (SqlConnection connection = GetConnection())
{
List<int> ilist = new List<int>();
//执行查询，获取结果集集合
var multi = connection.QueryMultiple(sql);
//遍历结果集
while(!multi.IsConsumed)
{
//读取当前结果集
var result = multi.Read().ToList()[0].A;
if (result != null)
{
ilist.Add(Convert.ToInt32(result));
}
}
//for(int i = 0;i<3;i++)
//{
// var result = multi.Read().ToList()[0].A;
// if (result != null)
// {
// ilist.Add(Convert.ToInt32(result));
// }
//}
foreach (var item in ilist)
{
Console.WriteLine(item.ToString());
}
}
Console.ReadLine();
}
}
11、如果某一代码中多次操作数据库，可以把conn设置为打开，最后时再close,
比如：
conn.open() conn.Query(..... ..... for.... ..... conn.close()
