? 根據(jù)設(shè)計(jì)當(dāng)MakeOld后（在讀取數(shù)據(jù)庫后，或者手動(dòng)調(diào)用），對記錄(SubSonic生成的類）屬性附值時(shí)，Sonic會(huì)檢測這個(gè)Value是否與原來的不同，只有值不同時(shí)才會(huì)附值成功，并將該列添加到DirtyColumns，而DirtyColumns中的列才會(huì)被Update采用，一般情況下 只要所有列中有一個(gè)列的是Dirty==true(被更改過），那么在Save時(shí)就會(huì)采用Update,

注意：SubSonic中判斷是否采用Update判斷“全部字段集合”中是否存在一個(gè)字段被更改，而生成Update命令時(shí)使用的集合是DirtyColumns集合，而不是直接從全部字段集合中查找那些被更改的字段，在多數(shù)情況下不會(huì)出問題，但有些時(shí)候可能帶來意想不到的問題，參考下面的場境3。

//=============參考代碼1================

??????????? public bool IsDirty
??????????? {
??????????????? get
??????????????? {
??????????????????? foreach(TableColumnSetting setting in this)
??????????????????? {
??????????????????????? if(setting.IsDirty)
??????????????????????????? return true;
??????????????????? }
??????????????????? return false;
??????????????? }
??????????????? //set
??????????????? //{
??????????????? //??? foreach (TableColumnSetting setting in this)
??????????????? //??????? setting.IsDirty = value;
??????????????? //}
??????????? }

//============參考代碼2============

???? public QueryCommand GetSaveCommand(string userName)
??????? {
??????????? if(IsNew)
??????????????? return GetInsertCommand(userName);

??????????? if(IsDirty)
??????????????? return GetUpdateCommand(userName);

??????????? return null;
??????? }

如果您對記錄未做任何更改而直接調(diào)用?.Save()時(shí)會(huì)根據(jù)IsNew與IsDirty的取值來決定采用Insert或Update。

如果兩個(gè)多是false，那么就返回null.那么Save操作將什么都不做。

//============參考代碼3============

?? QueryCommand cmd = GetSaveCommand(userName);
??????????????? if(cmd == null)
??????????????????? return;

場境1：

Employe emp=new Employe(1);//加載一個(gè)員工數(shù)據(jù)

//這個(gè)時(shí)候 IsNew=false,IsDirty=false

emp.Name=emp.Name; //沒有改變

emp.Save();//這里的Save方法將不做任何處理

?

場境2：

Employe emp=new Employe(1);

emp.Name=txtName.txt;//假設(shè)您在文本框中調(diào)整了Name取值

//這個(gè)時(shí)候 isNew=false;IsDirty=true;

emp.Save();將使用Update，并且只更新Name字段。

?

場境3:（報(bào)錯(cuò))

Employe emp=new Employe(1);

Employe backEmp=new Employe();

backEmp.CopyFrom(backEmp);

//copyFrom后會(huì)backEmp.IsDirty全部是true

//參考代碼7

backEmp.Name="xxxx";

backEmp.MackOld();//將IsNew設(shè)置成False

backEmp.Save(); //報(bào)錯(cuò)，IsDirty=True,而DirtyColumns為空，

//生成 Update Employe Set Where EmpoyeId=1 這樣的錯(cuò)誤TSQL

?

場境4:(報(bào)錯(cuò))

Employe emp=new Employe(1);

Employe backEmp=new Employe();

backEmp.CopyFrom(backEmp);

backEmp.MackOld();

backEmp.Name=backEmp.Name;

backEmp.Save();//這時(shí)IsDirty是True,而DirtyColumns為空

?

正確作法，應(yīng)該在backEmp.MackOld()；后再調(diào)用backEmp.MackClear();

//=============參考代碼8=================

????? /// <summary>
??????? /// Called after any property is set. Sets IsDirty to <c>true</c>.
??????? /// </summary>
??????? public void MarkClean()
??????? {
??????????? foreach(TableSchema.TableColumnSetting setting in columnSettings)
??????????????? setting.IsDirty = false;
??????????? DirtyColumns.Clear();
??????? }

//========參考代碼4==========

??????? /// <summary>
??????? /// Called after Update() invokation. Sets IsNew to <c>false</c>.
??????? /// </summary>
??????? public void MarkOld()
??????? {
??????????? IsLoaded = true;
??????????? _isNew = false;
??????? }

//========參考代碼5======================

??????? /// <summary>
??????? /// Copies the passed-in instance settings to this instance
??????? /// </summary>
??????? /// <param name="copyInstance">The copy instance.</param>
??????? public void CopyFrom(T copyInstance)
??????? {
??????????? if(copyInstance == null)
??????????????? throw new ArgumentNullException("copyInstance");

??????????? foreach(TableSchema.TableColumnSetting setting in copyInstance.columnSettings)
??????????????? SetColumnValue(setting.ColumnName, setting.CurrentValue);
??????? }

//========參考代碼6======================

??????? /// <summary>
??????? /// Sets a value for a particular column in the record
??????? /// </summary>
??????? /// <param name="columnName">Name of the column, as defined in the database</param>
??????? /// <param name="oValue">The value to set the type to</param>
??????? public void SetColumnValue(string columnName, object oValue)
??????? {
??????????? columnSettings = columnSettings ?? new TableSchema.TableColumnSettingCollection();

??????????? // add the column to the DirtyColumns
??????????? // if this instance has already been loaded
??????????? // and this is a change to existing values
??????????? if(IsLoaded && !IsNew)
??????????? {
??????????????? TableSchema.Table schema = GetSchema();
??????????????? object oldValue = null;
??????????????? string oldValueMsg = "NULL";
??????????????? string newValueMsg = "NULL";
??????????????? bool areEqualOrBothNull = false;

??????????????? try
??????????????? {
??????????????????? oldValue = columnSettings.GetValue(columnName);
??????????????? }
??????????????? catch {}

??????????????? if(oldValue == null && oValue == null)
??????????????????? areEqualOrBothNull = true;
??????????????? else
??????????????? {
??????????????????? if(oldValue != null)
??????????????????? {
??????????????????????? oldValueMsg = oldValue.ToString();
??????????????????????? areEqualOrBothNull = oldValue.Equals(oValue);
??????????????????? }

??????????????????? if(oValue != null)
??????????????????????? newValueMsg = oValue.ToString();
??????????????? }

??????????????? TableSchema.TableColumn dirtyCol = schema.GetColumn(columnName);

??????????????? if(dirtyCol != null && !areEqualOrBothNull)
??????????????? {
??????????????????? string auditMessage = String.Format("Value changed from {0} to {1}{2}", oldValueMsg, newValueMsg, Environment.NewLine);
??????????????????? TableSchema.TableColumn dirtyEntry = DirtyColumns.GetColumn(columnName);
??????????????????? if(dirtyEntry != null)
??????????????????? {
??????????????????????? DirtyColumns.Remove(dirtyEntry);
??????????????????????? auditMessage = String.Concat(dirtyCol.AuditMessage, auditMessage);
??????????????????? }

??????????????????? dirtyCol.AuditMessage = auditMessage;
??????????????????? DirtyColumns.Add(dirtyCol);
??????????????? }
??????????? }

??????????? columnSettings.SetValue(columnName, oValue);//這里最終調(diào)用參考代碼7

??????? }

//============參考代碼7============

??????????? /// <summary>
??????????? /// Gets or sets the current value.
??????????? /// </summary>
??????????? /// <value>The current value.</value>
??????????? public object CurrentValue
??????????? {
??????????????? get { return _currentValue; }
??????????????? set
??????????????? {
??????????????????? if(value == null && _currentValue == null)
??????????????????????? return;

??????????????????? if(value != null)
??????????????????? {
??????????????????????? if(value.Equals(_currentValue))
??????????????????????????? return;
??????????????????? }

??????????????????? _currentValue = value;
??????????????????? _isDirty = true;
??????????????? }
??????????? }

轉(zhuǎn)載于:https://www.cnblogs.com/wdfrog/archive/2010/06/30/1768159.html

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