an attempt to attach an auto-named database c#

Question

an attempt to attach an auto-named database c#

hamed algazaly 106

hello everyone..
my C# application with .mdf database works fine in my development machine ..
but when I try to run the program an another machine I receive this error message..

an attempt to attach an auto-named database for file <my development machine .mdf path> failed.
a database with the same name exists, or specified file cannot be opened, or it is located on UNC share.

this is my connection String
<add name="conn" connectionString="Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\mr-ho\source\repos\HighTopClinic\HighTopClinic\clincDB.mdf;Integrated Security=True"
providerName="System.Data.sqlclient" />

I'm using SqL LocalDB 2019

please help

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3 additional answers

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Answer 1

@hamed algazaly ，you could try the following steps to avoid the error you get when you access the database in another machine.

First, Please place your mdf file in your Winformapp/bin/debug folder.

Second, you could set the connection string by using DataDirectory in the App.Config.

<?xml version="1.0" encoding="utf-8" ?>  
<configuration>  
    <startup>   
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.8" />  
    </startup>  
  <connectionStrings>  
    <clear />  
    <add name="conn" connectionString="Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\School.mdf;Integrated Security=True"  
providerName="System.Data.sqlclient" />  
  </connectionStrings>  
   
</configuration>

Based on my test, I can connect the database successfully when I run the app in another computer.

Best Regards,
Jack

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Abu Khalid Rifat 0 Reputation points

2023-01-16T13:34:57.81+00:00

What is Winformapp ? Is it a directory ?

Answer 2

Bruce (SqlWork.com) 78,316 Volunteer Moderator

so on the other machine does

dir C:\Users\mr-ho\source\repos\HighTopClinic\HighTopClinic\clincDB.mdf

list a file and is it read/write. also check permissions.

hamed algazaly 106 Reputation points

2021-09-10T15:43:33.883+00:00

This path is in my development machine but is not exist in the other machine
Bruce (SqlWork.com) 78,316 Reputation points Volunteer Moderator

2021-09-10T19:55:54.017+00:00

a local db must be exist on the machine that will attach, no shares allowed. you need to copy the mdf to the other machine, and update the connection string to the path.

Answer 3

P a u l 10,761

Is the other machine a developer machine, or is it for a QA/staging/production environment?

hamed algazaly 106 Reputation points

2021-09-10T17:45:59.077+00:00

Just my brother pc that I'm trying to run the application on..

If it work in that pc that mean i can run it on any other pc
P a u l 10,761 Reputation points

2021-09-10T18:21:20.023+00:00

Is it required that you use an mdf file rather than you just hosting a SQL server instance and your brother's PC connects to it?
hamed algazaly 106 Reputation points

2021-09-10T18:37:06.897+00:00

It's an mdf file attached in my project
P a u l 10,761 Reputation points

2021-09-10T19:04:06.227+00:00
The problem with using attaching to an mdf file from multiple running apps is that when the first app connects it maintains an exclusive lock the file until the connection is closed, meaning the second instance may not be able to connect/may have to be made more fault tolerant to account for file locks.

You have several options though:

Create a new service/API that acts as the Data Access Layer of both instances of the app. If either apps want to read/write from/to the DB they need to send the request to the Data Access Layer.

(preferred) Host a SQL server instance within your network (or on your own PC) and you and your brother can share a single instance running in the SQL Server Engine.

(untested) Not entirely sure how practical this suggestion is, but perhaps just sharing the mdf file over your home network to your brother's PC? You'll still have the file locking issue, but if you add User Instance=true to your brother's connection string it will create a copy of your original database for his instance of the application.

Similar to the point above, except you write to the same mdf file and manage the file locks. Make sure you close your connections as soon as you're done with them, and add retries for when a connection failed to establish.
hamed algazaly 106 Reputation points

2021-09-10T19:51:22.933+00:00

I want the application to be running in any other pc with
.mdf and SQL express localdb

Answer 4

Erland Sommarskog 122.7K MVP Volunteer Moderator

It seems that you want the same database to be accessible from the two different machines. Then you cannot use LocalDB which is only for local database. You need to install SQL Server Express. The connection string should not have this funny AttachDBFilename, but you simply create and set up the database within your instance, and the conntiction string should read:

Server=YOURMACHINE\SQLEXPRESS;Initial Catalog=YourDB;Integrated Security=SSPI

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an attempt to attach an auto-named database c#

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