C# 应用

1. 引入库类
2. 连接数据库
3. 访问数据库
   1）增删改数据库
   2）查数据库
4. 数据转换
5. 事务

1. 引入库类

引入 Npgsql.dll

using Npgsql;  
using NpgsqlTypes;

2. 连接数据库

/// <summary>
/// 使用固定连接进行数据库的操作，默认false，表示每次操作都使用新的连接,true,表示数据库操作都使用变量NpgsqlConn，设置为true时必须初始化NpgsqlConn
/// </summary>
public bool UseSpecifiedConn = false;

/// <summary>
/// 使用指定连接执行数据库操作时所用的数据库连接，使用前需设置UseSpecifiedConn，并且自行管理连接的打开和关闭
/// </summary>
public NpgsqlConnection NpgsqlConn;

using Npgsql;
using NpgsqlTypes;
...
public void SetConnectStr(string connStr)
{
    SetConnectStr(connStr, false);
}

/// <summary>
/// 构造函数，如果固定连接，初始化 NpgsqlConn；如果不固定，只需要设置 ConnectionString 连接信息。当然，也可以不判断，直接执行。
/// </summary>
/// <param name="connStr"></param>
/// <param name="IsUseSpecifiedConn">是否使用固定连接，用于事务</param>
public void SetConnectStr(string connStr, bool IsUseSpecifiedConn)
{
    if (IsUseSpecifiedConn)
    {
        UseSpecifiedConn = IsUseSpecifiedConn;
        NpgsqlConn = new NpgsqlConnection(connStr);
    }
    else
    {
        ConnectionString = connStr;
    }
}

/// <summary>
/// 关闭数据库连接
/// </summary>
/// <returns></returns>
public bool CloseConn()
{
    try
    {
        NpgsqlConn.Close();
        return NpgsqlConn.State == ConnectionState.Closed;
    }
    catch (Exception ex)
    {
        Common.WriteLog.Error("关闭数据库连接出错!", ex);
        return false;
    }
}

/// <summary>
/// 检查数据库连接是否正常
/// </summary>
/// <returns></returns>
public bool TryOpenConn()
{
    bool result = false;
    using (NpgsqlConnection NpgsqlConn = new NpgsqlConnection(ConnectionString))
    {
        try
        {
            NpgsqlConn.Open();
            result = NpgsqlConn.State == ConnectionState.Open;
        }
        catch (Exception ex)
        {
            Common.WriteLog.Error("打开数据库连接出错!", ex);
        }
    }
    return result;
}

3. 访问数据库

3.1 增删改数据库

3.1.1 返回 int

/// <summary>
/// 增删改 postgre 数据库，返回是否成功标识
/// </summary>
/// <param name="sqlText"></param>
/// <returns></returns>
public int ExecuteNonQuery(string sqlText)
{
    return ExecuteNonQuery(sqlText, null);
}

/// <summary>
/// 增删改 postgre 数据库，返回是否成功标识
/// </summary>
/// <param name="sqlText"></param>
/// <param name="param">参数集合</param>
/// <returns></returns>
public int ExecuteNonQuery(string sqlText, NpgsqlParameter[] param)
{
    int result = int.MinValue;
    NpgsqlConnection conn = UseSpecifiedConn ? NpgsqlConn : new NpgsqlConnection(ConnectionString);
    using (var nSqlCommand = new NpgsqlCommand(sqlText, conn))
    {
        try
        {
            if (conn.State != ConnectionState.Open)
            {
                conn.Open();
            }
            // 添加参数
            if (param != null)
            {
                SetParmDBNull(param);
                nSqlCommand.Parameters.AddRange(param);
            }
            // 执行查询并返回受影响的行数
            result = nSqlCommand.ExecuteNonQuery();
        }
        catch (NpgsqlException ex)
        {
            Common.WriteLog.Error("执行数据库语句出错!执行语句:" + sqlText, ex);
            if (ex != null)
            {
                result = ex.ErrorCode;
            }
        }
        finally
        {
            if (!UseSpecifiedConn)
            {
                conn.Dispose();
            }
        }
    }
    return result;
}

/// <summary>
/// 将参数中null值转换为DBNull
/// </summary>
/// <param name="param"></param>
public void SetParmDBNull(NpgsqlParameter[] param)
{
    foreach (var p in param)
    {
        if (p.Value == null)
        {
            p.Value = DBNull.Value;
        }
    }
}

3.1.2 增删改调用实例

/// <summary>
/// 插入xx
/// </summary>
/// <param name="cameraid">摄像头ID</param>
/// <param name="itag">标签</param>
/// <returns></returns>
public int InsertAXX(string cameraid, ExtendCustomTag itag)
{
    if (string.IsNullOrEmpty(cameraid) || itag == null) return -1;

    string sql = "insert into TableName(CameraID,TagLevel) values(@CameraID,@TagLevel)";
    NpgsqlParameter[] param = new NpgsqlParameter[2];
    param[0] = new NpgsqlParameter("@CameraID", NpgsqlDbType.Text) { Value = cameraid };
    param[1] = new NpgsqlParameter("@TagLevel", NpgsqlDbType.Integer) { Value = itag.Level };

    int result = ExecuteNonQuery(sql, param);
    return result;
}

/// <summary>
/// 软删除xx
/// </summary>
/// <param name="presetId"></param>
/// <returns> 1 表示操作成功，-1 表示失败</returns>
public int DeleteAXX(string id)
{
    int flag = -1;
    if (!string.IsNullOrEmpty(id))
    {
        var deleteSql = string.Format("update tablename set status = false where id = '{0}'", id);
        flag = this.ExecuteNonQuery(deleteSql);
    }
    return flag;
}

3.2 查数据库

3.2.1 返回 datatable

/// <summary>
/// 查询 postgre 数据库，返回 DataTable 数据
/// </summary>
/// <param name="sqlText">sql查询语句</param>
/// <returns></returns>
public DataTable ExecuteQuery(string sqlText)
{
    return ExecuteQuery(sqlText, null);
}

/// <summary>
/// 查询 postgre 数据库，返回 DataTable 数据
/// </summary>
/// <param name="sqlText">sql查询语句</param>
/// <param name="param">参数集合</param>
/// <returns></returns>
public DataTable ExecuteQuery(string sqlText, NpgsqlParameter[] param)
{
    var dt = new DataTable();
    NpgsqlConnection conn = UseSpecifiedConn ? NpgsqlConn : new NpgsqlConnection(ConnectionString);
    using (var nda = new NpgsqlDataAdapter(sqlText, conn))
    {
        try
        {
            if (param != null)
            {
                SetParmDBNull(param);
                nda.SelectCommand.Parameters.AddRange(param);
            }
            var ds = new DataSet();
            nda.Fill(ds);
            dt = ds.Tables[0];
        }
        catch (Exception ex)
        {
            Common.WriteLog.Error("查询数据库出错!查询语句:" + sqlText, ex);
        }
        finally
        {
            if (!UseSpecifiedConn)
            {
                conn.Dispose();
            }
        }
    }
    return dt;
}

2.2.2 返回 int

/// <summary>
/// 查询唯一值（用来查总记录数等等..）
/// </summary>
/// <param name="sqlText"></param>
/// <returns></returns>
public int QueryOnly(string sqlText)
{
    NpgsqlConnection conn = UseSpecifiedConn ? NpgsqlConn : new NpgsqlConnection(ConnectionString);
    try
    {
        if (conn.State != ConnectionState.Open)
        {
            conn.Open();
        }
        NpgsqlCommand objCommand = new NpgsqlCommand(sqlText, conn);
        
        //结果集中的第一行第一列
        int count = Convert.ToInt32(objCommand.ExecuteScalar());
        return count;
    }
    catch (Exception e)
    {
        Console.WriteLine(e.Message);
        return 0;
    }
    finally
    {
        if (!UseSpecifiedConn)
        {
            conn.Dispose();
        }
    }
}

3.2.3 查数据库实例

/// <summary>
/// 获取指定摄像头的标签
/// </summary>
/// <param name="cameraid">摄像头编码</param>
/// <returns></returns>
public DataTable SelectTag(string cameraid)
{
    string sql = "select CameraID,TagName,TagLevel,TagLink,TagPTStr,TagDirection from Tag where CameraID=@CameraID";
    NpgsqlParameter[] param = new NpgsqlParameter[1];
    param[0] = new NpgsqlParameter("@CameraID", NpgsqlDbType.Text) { Value = cameraid };
    return ExecuteQuery(sql, param);
}

/// <summary>
/// 获取 xxx
/// </summary>
/// <param name="cameraEncode"></param>
/// <returns></returns>
public List<Preset> SelectPresetBy(string cameraEncode)
{
    var list = new List<Preset>();
    try
    {
        if (string.IsNullOrEmpty(cameraEncode))
        {
            throw new Exception("cameraId 为空");
        }
        string selectSql = string.Format("select * from preset where cameraencode = '{0}' order by id asc", cameraEncode);
        var dt = this.ExecuteQuery(selectSql);
        list = DataTableToList<Preset>(dt).ToList();
    }
    catch (Exception ex)
    {
        Common.WriteLog.Error("查找预置位列表出错!", ex);
    }
    return list;
}

public int CheckPoliceSchedule(DateTime checktime)
{
    int res = -1;
    try
    {
        var sqlText = string.Format("select COUNT(*) sum from xx where endtime>to_timestamp('{1}','yyyy-MM-dd HH24:MI:SS')", checktime.ToString("yyyy-MM-dd HH:mm:ss"));
        res = QueryOnly(sqlText);
    }
    catch (Exception ex)
    {
        Common.WriteLog.Error("xx出错!", ex);
    }
    
    return res;
}

4. 将 datatable 转成对象

/// <summary>
/// DataTable转换List，反射机制
/// </summary>
/// <param name="dt"></param>
/// <returns></returns>
public IList<T> DataTableToList<T>(DataTable dt) where T : new()
{

    IList<T> list = new List<T>();// 定义集合
    Type type = typeof(T); // 获得此模型的类型
    var tempName = string.Empty;
    foreach (DataRow dr in dt.Rows)
    {
        T t = new T();
        PropertyInfo[] propertys = t.GetType().GetProperties();// 获得此模型的公共属性
        foreach (PropertyInfo pi in propertys)
        {
            tempName = pi.Name;
            if (dt.Columns.Contains(tempName))
            {
                if (!pi.CanWrite) continue;
                object value = dr[tempName];
                if (value != DBNull.Value)
                    pi.SetValue(t, value, null);
            }
        }
        list.Add(t);
    }
    return list;
}

/// <summary>
/// 确认 DataTable 里面最多只有一行数据，转成 Object，反射机制
/// </summary>
/// <param name="dt"></param>
/// <returns></returns>
public T DataTableToObject<T>(DataTable dt) where T : new()
{
    T t = new T();
    var tempName = string.Empty;
    if (dt.Rows == null || dt.Rows.Count == 0)
    {
        return t;
    }

    DataRow dr = dt.Rows[0];

    PropertyInfo[] propertys = t.GetType().GetProperties();// 获得此模型的公共属性
    foreach (PropertyInfo pi in propertys)
    {
        tempName = pi.Name;
        if (dt.Columns.Contains(tempName))
        {
            if (!pi.CanWrite) continue;
            object value = dr[tempName];
            if (value != DBNull.Value)
                pi.SetValue(t, value, null);
        }
    }

    return t;
}

5. 事务

public class PostgreSqlDao
{
    /// <summary>
    /// 打开数据库连接
    /// </summary>
    /// <returns></returns>
    public bool OpenConn()
    {
        try
        {
            if (NpgsqlConn.State == ConnectionState.Open)
            {
                return true;
            }
            else
            {
                NpgsqlConn.Open();
                return NpgsqlConn.State == ConnectionState.Open;
            }
        }
        catch (Exception ex)
        {
            Common.WriteLog.Error("打开数据库连接出错!", ex);
            return false;
        }
    }
    ...
}

// 事务使用
public bool Transaction()
{
    bool res = false;
    PostgreSqlDao pg = new PostgreSqlDao(Common.ConnectString, true);
    
    if (pg.OpenConn())
    {
        // 新建一个事务
        var trans = pg.NpgsqlConn.BeginTransaction();
        try
        {
            foreach (var x in XX)
            {
                // 执行数据写入操作
            }
            
            // 提交事务
            trans.Commit();
            res = true;
        }
        catch (Exception ex)
        {
            // 回滚事务
            trans.Rollback();
        }
        finally
        {
            // 关闭连接
            pg.CloseConn();
        }
    }
    return res;
}

 /// <summary>
/// 执行多条SQL语句，实现数据库事务。
/// </summary>
/// <param name="SQLStringList">多条SQL语句</param> 
public bool ExecuteTransSQL(List<String> SQLStringList)
{
    using (NpgsqlConnection conn = UseSpecifiedConn ? NpgsqlConn : new NpgsqlConnection(ConnectionString))
    {
        if (conn.State != ConnectionState.Open)
            conn.Open();
        NpgsqlCommand cmd = new NpgsqlCommand();
        cmd.Connection = conn;
        NpgsqlTransaction tx = conn.BeginTransaction();
        cmd.Transaction = tx;
        try
        {
            int count = 0;
            for (int n = 0; n < SQLStringList.Count; n++)
            {
                string strsql = SQLStringList[n];
                if (strsql.Trim().Length > 1)
                {
                    cmd.CommandText = strsql;
                    count += cmd.ExecuteNonQuery();
                }
            }
            tx.Commit();
            return true;
        }
        catch (Exception ex)
        {
            tx.Rollback();
            return false;
        }
        finally
        {
            if (!UseSpecifiedConn)
            {
                conn.Dispose();
            }
        }
    }
}