在做三层架构的时候，特别是对表做查询的时候，有时候并不确定查询条件的个数，比如查询学生表：有可能只输入学号，或者姓名，或者性别，总之查询条件的参数个数并不确定，下面是我用List实现传值的代码：

附图如下:

在这里附上数据库的表结构：

CREATE TABLE Student(
        StuId        VARCHAR(6) PRIMARY KEY,
        StuName   VARCHAR(10) NOT NULL,
        MajorId     INT NOT NULL,
        Sex           VARCHAR(2) NOT NULL DEFAULT '男',
        Birthdate   SMALLDATETIME NOT NULL,
        Credit        FLOAT,
        Remark     VARCHAR(200)
)

------------------------------------------------------------------------------------------------

程序代码如下：

Model层----------------------------------------------包含两个类------------------------

------------------表的实体类Student-----------------

public class Student
    {
        private string stuId; 
        public string StuId
        {
            get { return stuId; }
            set { stuId = value; }
        }

private string stuName;

public string StuName

{

get { return stuName; }

set { stuName = value; }

}

private int majorId;

public int MajorId

{

get { return majorId; }

set { majorId = value; }

}

private string sex;

public string Sex

{

get { return sex; }

set { sex = value; }

}

private DateTime birthdate;

public DateTime Birthdate

{

get { return birthdate; }

set { birthdate = value; }

}

private float credit;

public float Credit

{

get { return credit; }

set { credit = value; }

}

private string remark;

public string Remark

{

get { return remark; }

set { remark = value; }

}

}

------------------Condition主要用于传递参数，这个类也可以定义在别的地方-------------------

public class Condition
    {
        public string paramName { get; set; }
        public string paramValue { get; set; }
        public ConditionOperate Operation { get; set; }

// 查询所用到的运算操作符
        public enum ConditionOperate : byte
        {
            Equal,           // 等于
            NotEqual,      // 不等于
            Like,             // 模糊查询
            Lessthan,      // 小于等于
            GreaterThan  // 大于
        }
    }

---------------------DAL层-----------------------------------------------------------------

------------------DBHelper类---------------------------------------------

public class DBHelper

{

private SqlConnection conn;

private SqlCommand cmd;

private SqlDataAdapter sda;

private DataSet ds;

public DBHelper()

{

conn = new SqlConnection(ConfigurationManager.ConnectionStrings["key"].ConnectionString);

}

// 不带参数的查询

public DataSet GetResult(string sql, CommandType type)

{

cmd = new SqlCommand(sql, conn);

sda = new SqlDataAdapter(cmd);

conn.Close();

ds = new DataSet();

sda.Fill(ds, "student");

return ds;

}

// 带参数的查询

public DataSet GetResult(string sql, CommandType type, params SqlParameter[] paras)

{

cmd = new SqlCommand(sql, conn);

if (type == CommandType.StoredProcedure)

{

cmd.CommandType = CommandType.StoredProcedure;

}

cmd.Parameters.AddRange(paras);

sda = new SqlDataAdapter(cmd);

conn.Close();

ds = new DataSet();

sda.Fill(ds, "student");

return ds;

}

}

-----------------------------对Student表操作类

public class StudenDAL

{

public DataSet GetStudent(List<Condition> condition)

{

DataSet ds = new DataSet();

DBHelper db = new DBHelper();

string sql = "select * from student";

// 如果带查询语句带参数

if (condition.Count > 0)

{

sql += SqlString(condition);

ds = db.GetResult(sql, CommandType.Text, SqlParas(condition));

}

else

{

ds = db.GetResult(sql, CommandType.Text);

}

return ds;

}

----------------------以下两个可以写成一个类，以便如果有多张表时，可以实现代码的复用----------------------------------

// 获取查询参数

public SqlParameter[] SqlParas(List<Condition> cond)

{

List<SqlParameter> paras = new List<SqlParameter>();

for (int i = 0; i < cond.Count; i++)

{

SqlParameter para = new SqlParameter("@" + cond[i].paramName, cond[i].paramValue);

if (cond[i].Operation == Condition.ConditionOperate.Like)

{

para.SqlValue = "%" + cond[i].paramValue + "%";

}

paras.Add(para);

}

return paras.ToArray();

}

// 获取SQL查询语句的where子句

public string SqlString(List<Condition> cond)

{

string sqlWhere = string.Empty;

List<string> where = new List<string>();

// 数组元素的顺序应该与ConditionOperate枚举值顺序相同

string[] operateType = { " = ", " <> ", " Like ", " <= ", " >= " };

for (int i = 0; i < cond.Count; i++)

{

int index = (int)cond[i].Operation;

where.Add(string.Format("{0}" + operateType[index] + "{1}", cond[i].paramName, "@" + cond[i].paramName));

}

sqlWhere = " where " + string.Join(" and ", where.ToArray());

return sqlWhere;

}

}

------------------------------BLL层---------------------------

public class StudentBLL
    {
        private readonly StudenDAL stuDal = new StudenDAL();
        public DataSet GetStudent(List<Condition> condition)
        {
            return stuDal.GetStudent(condition);
        }
    }

------------------------------UI层，查询按钮的单击事件-------------------------------------

protected void btnSearch_Click(object sender, EventArgs e)

{

Condition condition;

StudentBLL stu = new StudentBLL();

List<Condition> list = new List<Condition>();

if (txtId.Text!="")

{

condition = new Condition()

{

paramName = "stuId",

paramValue = txtId.Text,

Operation = Condition.ConditionOperate.Equal

};

list.Add(condition);

}

if (txtName.Text!="")

{

condition = new Condition()

{

paramName = "stuName",

paramValue = txtName.Text,

Operation = Condition.ConditionOperate.Equal

};

list.Add(condition);

}

if (txtSex.Text != "")

{

condition = new Condition()

{

paramName = "Sex",

paramValue = txtSex.Text,

Operation = Condition.ConditionOperate.Equal

};

list.Add(condition);

}

GridView1.DataSource = stu.GetStudent(list);

GridView1.DataBind();

}