初识ORM框架——Dapper

Dapper框架

Dapper是一个轻量级的ORM框架，它扩展了IDbConnection接口的功能，适合多种数据库。

先定义一个类，注意一定要使用属性

class Student
{
    public Guid ID { get; set; }
    public string Name { get; set; }
}

Sql语句，注意GUID，必须设置为char(36)不能设置为varchar(36).

CREATE TABLE `Student` (
    `Name`  varchar(63),
    `ID`    char(36) NOT NULL,
    PRIMARY KEY(ID)
);

连接

public static SQLiteConnection GetDBConnection()
{
    try
    {
        SQLiteConnectionStringBuilder sb = new SQLiteConnectionStringBuilder();
        sb.DataSource = System.Configuration.ConfigurationManager.ConnectionStrings["dbPath"].ConnectionString;
        SQLiteConnection conn = new SQLiteConnection(sb.ToString());
        return conn;
    }
    catch (Exception ex)
    {
        throw ex;
    }
}

由于SQLiteConnection继承了IDisposable接口，于是每次调用都可以用

using (SQLiteConnection con = DBHelper.GetDBConnection())
{
    //代码写这
}

insert

//GUID在数据库中我是以char(36)保存的，因此不能保存guid类型，应该转换为string类型
string sqlStr = "insert into Student(ID,Name) Values(@ID,@Name)";
con.Execute(sqlStr, new { ID= Guid.NewGuid().ToString("N") , Name = "张三" });

当然了，也可以插入已经实例化的Student类

Student student = New Student（）{ ID= Guid.NewGuid().ToString("N") , Name = "张三" };
string sqlStr = "insert into Student(ID,Name) Values(@ID,@Name)";
con.Execute(sqlStr, student );

delete

string sqlStr = "delete from Student WHERE id =@id";
con.Execute(sqlStr , student );

update

string sqlStr = "update Student set Name=@name WHERE id =@id";
con.Execute(sqlStr , student );

select

string sqlStr = "select ID,Name from Student";
List<Student> studentLists = con.Query<Student>(sqlStr).ToList();
//注意：会报错，类中的guid类型跟数据库中的string类型不符合

应该改sql语句加上这个Student类

string sqlStr = "select ID as IDString,Name from Student";//通过别名将值保存为IDString
List studentLists = con.Query(sqlStr).ToList();

class Student
{
    public Guid ID { get; set; }
    public string Name { get; set; }
    private string IDString//设置为private比较安全，除了select以外没有需要这个属性的地方
    {
        get { return ID.ToString("N"); }
        set { ID = new Guid(value); }
    }
}

抽象类的select

类为抽象类

abstract class Student
{
    public Guid ID { get; set; }
    public string Name { get; set; }
    private string IDString//设置为private比较安全，除了select以外没有需要这个属性的地方
    {
        get { return ID.ToString("N"); }
        set { ID = new Guid(value); }
    }
}

class A:Student
{

}
class B:Student
{

}

如果按照上面select的方法会说抽象类无法实例化，那么就下面这个方法解决，先增加两个扩展方法

public static Student ConvertToStudent(object value)
{
    var dapperRowProperties = value as IDictionary<string, object>;
    //从查询来的Name中来判断实例化为A还是B
    switch (dapperRowProperties["Name"].ToString())
    {
        case “A”: return GetObject(dapperRowProperties);
        case "B": return GetObject(dapperRowProperties);
        default:  return null;
    }
}
private static T GetObject(IDictionary<string, object> dict)
{
    Type type = typeof(T);
    var obj = Activator.CreateInstance(type);

    foreach (var kv in dict)
    {
        //反射，非public属性不会被找到,所以要传入BindingFlags参数来获取protected属性
        type.GetProperty(kv.Key,System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic).SetValue(obj, kv.Value);
    }
    return (T)obj;
}

然后就可以查询了

string sqlStr = "select ID as IDString,Name from Student";
List studentLists = con.Query(sqlStr).Select(ConvertToStudent).ToList();

保存到datatable

添加一个扩展方法

public static DataTable ToDataTable(this IEnumerable items)
{
    var data = items.ToArray();
    if (data.Count() == 0) return null;

    var dt = new DataTable();
    foreach (var key in ((IDictionary<string, object>)data[0]).Keys)
    {
        dt.Columns.Add(key);
    }
    foreach (var d in data)
    {
        dt.Rows.Add(((IDictionary<string, object>)d).Values.ToArray());
    }
    return dt;
}

然后就能查找出datatable类型的数据了

string sqlStr = "select ID as IDString,Name from Student";
DataTable dt = DBHelper.ToDataTable(con.Query(sqlStr));

其实还有些多表查询，多结果查询等没讲，等之后再补充