插入重複記錄LINQ

Question

我試圖插入使用下面的LINQ查詢。不知何故，我得到了ID的重複記錄。有人能幫我解釋細節嗎？

try { 
OLA_ASSESSMENT_DTL OAD = db.OLA_ASSESSMENT_DTL.SingleOrDefault(
    ev => ev.OAD_RIV_ID == id); 

transaction = "Modify"; // resetting the value of the variable 
if (OAD == null) { 
    transaction = "Add"; 
    OAD = new OLA_ASSESSMENT_DTL(); 
} 
OAD.OAD_PER_RELAIONSHIP = relationshipfocus.relationshipfocus; 
OAD.OAD_PER_RELAIONSHIP_COMMENT = CRecHelper.CheckIsNullString(relationshipfocus.strrelationshipfocus).ToString(); 
OAD.OAD_RIV_ID = id;  
OAD.OAD_MODIFIED_DATE = DateTime.Now; 
if (transaction == "Add") { 
    db.OLA_ASSESSMENT_DTL.Add(OAD); 
} 
db.SaveChanges(); 
} 

Answer 1

起初，你正確地檢測重複記錄（雖然你可能應該使用FirstOrDefault代替SingleOrDefault，但是這是一個細節）：

OLA_ASSESSMENT_DTL OAD = db.OLA_ASSESSMENT_DTL.SingleOrDefault(
     ev => ev.OAD_RIV_ID == id); 

transaction = "Modify"; // resetting the value of the variable 
if (OAD == null) 
{ 
    transaction = "Add"; 
    OAD = new OLA_ASSESSMENT_DTL(); 
} 

但後來，你隨便的ID分配給對象即使你知道這是一個重複：

OAD.OAD_RIV_ID = id; 

首先，刪除了這一行，因爲它是無用的：

• 如果記錄已經存在，那麼你只是覆蓋ID與當前值
• 如果記錄是重複的，那麼你設置的新的記錄重複的ID

相反，設置一個唯一的ID，當你知道的記錄是重複的，下面您爲表定義爲準策略：

OLA_ASSESSMENT_DTL OAD = db.OLA_ASSESSMENT_DTL.SingleOrDefault(
     ev => ev.OAD_RIV_ID == id); 

transaction = "Modify"; // resetting the value of the variable 
if (OAD == null) 
{ 
    transaction = "Add"; 
    OAD = new OLA_ASSESSMENT_DTL(); 
    // TODO: Assign a unique id, or let the database assign one if the column is auto-increment 
}