C# 你如何检查记录是否存在
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/13830928/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How do you check if Record exists
提问by Hymanncoke
I have a form that does an insert. I want to see if the record already exists in the database to prevent duplicates. I am a little unsure of when this has to go down. In the codebehind for the controls that is the form or in the Class that I call on to perform the insert. Below is the class that is where I am thinking it goes.
我有一个可以插入的表单。我想查看该记录是否已存在于数据库中以防止重复。我有点不确定什么时候必须下降。在作为表单的控件的代码隐藏中或在我调用以执行插入的类中。下面是我认为它去的班级。
public class AddContacts
{
public int AddContact(string ContactName)
{
var myContact = new Solutions.Models.Contact();
myContact.ContactName = ContactName;
ItemContext _db = new ItemContext();
_db.Contacts.Add(myContact);
_db.SaveChanges();
return myContact.ContactID;
}
}
I have seen it done with If statements that use .Any()but i cannot get it work right. Nor do I understand what it would need to return in order for me to post a error message Contact Name already exists.
我已经看到它使用 If 语句完成，.Any()但我无法使其正常工作。我也不明白它需要返回什么才能发布错误消息Contact Name already exists。
采纳答案by siger
You could use the Any method like this:
您可以像这样使用 Any 方法：
bool contactExists = _db.Contacts.Any(contact => contact.ContactName.Equals(ContactName));
if (contactExists)
{
return -1;
}
else
{
_db.Contacts.Add(myContact);
_db.SaveChanges();
return myContact.ContactID;
}
The method calling AddContact would check the return value and decide whether to display an error or confirmation message to the user.
调用 AddContact 的方法将检查返回值并决定是否向用户显示错误或确认消息。
回答by Arash Emami
Do a check like this:
做这样的检查：
bool doesExistAlready = _db.Contacts.Any(o => o.ContactName == ContactName);
If that doesn't work, try this:
如果这不起作用，请尝试以下操作：
bool doesExistAlready = _db.Contacts.Count(o => o.ContactName == ContactName) > 0;
Turn on SQL tracing/debugging so you see the actual sql being produced.
打开 SQL 跟踪/调试，以便您看到正在生成的实际 sql。
回答by user5634773
This too can help.
这也可以提供帮助。
bool doesExistAlready = _db.Contacts.Count(o => o.ContactName == ContactName) > 0;
