在数据写入到数据库时，通常要根据某些条件检测记录是否存在，然后决定是否要写入，数据写入分两种情形：新添加数据和更新数据，在通用权限底层中，对这类判断进行了封装。
/// <summary>
/// 判断存在
/// </summary>
/// <param name="parameters"></param>
/// <param name="id"></param>
/// <returns></returns>
public virtual bool Exists(List<KeyValuePair<string, object>> parameters, object id = null)
{
bool result = false;
if (id != null)
{
result = DbLogic.Exists(DbHelper, this.CurrentTableName, parameters, new KeyValuePair<string, object>(this.PrimaryKey, id));
}
else
{
result = DbLogic.Exists(DbHelper, this.CurrentTableName, parameters);
}
return result;
}
/// <summary>
/// 记录是否存在
/// </summary>
/// <param name="dbHelper">数据库连接</param>
/// <param name="tableName">目标表名</param>
/// <param name="parameters">参数</param>
/// <param name="targetField">获取字段</param>
/// <param name="name">目标字段名</param>
/// <param name="parameters">目标字段值</param>
/// <returns>存在</returns>
public static bool Exists(IDbHelper dbHelper, string tableName, List<KeyValuePair<string, object>> parameters, KeyValuePair<string, object> parameter = new KeyValuePair<string, object>())
{
return GetCount(dbHelper, tableName, parameters, parameter) > 0;
}
/// <summary>
/// 获取个数
/// </summary>
/// <param name="dbHelper">数据库连接</param>
/// <param name="tableName">目标表名</param>
/// <param name="parameters">目标字段,值</param>
/// <returns>行数</returns>
public static int GetCount(IDbHelper dbHelper, string tableName, List<KeyValuePair<string, object>> parameters, KeyValuePair<string, object> parameter = new KeyValuePair<string, object>())
{
int result = 0;
string sqlQuery = "SELECT COUNT(1) "
+ " FROM " + tableName
+ " WHERE " + GetWhereString(dbHelper, parameters, BaseBusinessLogic.SQLLogicConditional);
if (!string.IsNullOrEmpty(parameter.Key))
{
if (parameter.Value != null)
{
sqlQuery += BaseBusinessLogic.SQLLogicConditional + "( " + parameter.Key + " <> ‘" + parameter.Value + "‘ ) ";
}
else
{
sqlQuery += BaseBusinessLogic.SQLLogicConditional + "( " + parameter.Key + " IS NOT NULL) ";
}
}
object returnObject = null;
if (parameters != null)
{
returnObject = dbHelper.ExecuteScalar(sqlQuery, dbHelper.MakeParameters(parameters));
}
else
{
returnObject = dbHelper.ExecuteScalar(sqlQuery);
}
if (returnObject != null)
{
result = int.Parse(returnObject.ToString());
}
return result;
}
该方法支持多种数据库(Oracle、MySQL、MSSQL等)，id为记录的主键，新增时是null。可以参照引入到自己项目中。
如在新增公司时，要求公司编号和公司名称不可以重复，前端文本框值变化时使用了Ajax异步判断。
/// <summary> /// 验证公司编号是否重复 /// </summary> /// <param name="code"></param> /// <param name="id"></param> /// <returns></returns> private bool ValidateCode(string code, string id) { code = DbLogic.SqlSafe(code); id = DbLogic.SqlSafe(id); return !organizeManager.Exists(new KeyValuePair<string, object>(BaseOrganizeEntity.FieldCode, code), id); } /// <summary> /// 验证公司名称是否重复 /// </summary> /// <param name="name"></param> /// <param name="id"></param> /// <returns></returns> private bool ValidateName(string name, string id) { name = DbLogic.SqlSafe(name); id = DbLogic.SqlSafe(id); return !organizeManager.Exists(new KeyValuePair<string, object>(BaseOrganizeEntity.FieldFullName, name), id); }
在新增公司时，Id为null，更新时传入公司的主键Id。
有了这个方法，表中记录存在判断处理就方便多了，而且支持增加多种条件的限制判断（参数List<KeyValuePair<string, object>> parameters）。
原文：http://www.cnblogs.com/hnsongbiao/p/5215122.html