MySQL通过实例化对象参数查询实例讲解

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public static string QueryByEntity<T>(T t) where T : new(){  string resultstr = string.Empty;  MySqlDataReader reader = null;  try  {    Type type = typeof(T);    PropertyInfo[] properties = type.GetProperties();    string select = string.Format("Select * from {0} {1}", type.Name, "{0}");    string where = string.Empty;    foreach (PropertyInfo property in properties)    {      var value = t.GetPropertyValue<T>(property);      if (value != null && !value.Equals(property.GetDefaultValue()))      {        if (string.IsNullOrEmpty(where))        {          where = string.Format(" where {0}='{1}' ", property.Name, value);        }        else        {          where = string.Format(" {0} and {1} = '{2}' ", where, property.Name, value);        }      }    }    select = string.Format(select, where);     MySqlConnection connection = OpenConnection();    if (connection == null)      return resultstr;    MySqlCommand _sqlCom = new MySqlCommand(select, connection);    reader = _sqlCom.ExecuteReader();    List<T> tList = new List<T>();    while (reader.Read())    {      T t1 = new T();      foreach (PropertyInfo property in properties)      {        if (!string.IsNullOrEmpty(reader[property.Name].ToString()))        {          property.SetMethod.Invoke(t1, new object[] { reader[property.Name] });        }      }      tList.Add(t1);    }    resultstr = JsonConvert.SerializeObject(tList);  }  catch (Exception ex)  {    Logging.Error(string.Format("查询数据库失败，{0}", ex.Message));  }  finally  {    if (reader != null)    {      reader.Close();      reader.Dispose();    }  }  return resultstr;}internal static class ObjectExtend{  public static object GetPropertyValue<T>(this object obj, PropertyInfo property)  {    Type type = typeof(T);    PropertyInfo propertyInfo = type.GetProperty(property.Name);    if (propertyInfo != null)    {      return propertyInfo.GetMethod.Invoke(obj, null);    }    return null;  }  public static object GetDefaultValue(this PropertyInfo property)  {    return property.PropertyType.IsValueType ? Activator.CreateInstance(property.PropertyType) : null;  }}

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