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Posted 25 Mar 2013

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How to fix Column 'InvariantName' is constrained to be unique

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25 Mar 2013CPOL1 min read
The build of Web.Debug.Config throws the error as value 'MySql.Data.MySqlClient' is already present.


When you build a web project that uses Enterprise Library Community for the Application Data Block and the MySQL .NET / Connector, VisualStudio throws the error  "Column 'InvariantName' is constrained to be unique. Value 'MySql.Data.MySqlClient' is already present", but you added it only once. 

Is very simple to fix, you need to add "<remove invariant="MySql.Data.MySqlClient"></remove>" to the start of > DbProviderFactories node. 


You can be confused if you used XML transform for Web.Config, Web.Debug.Config or Web.Release.Config.

But you shouldn't focus in that. The problem is the provider's installation put in machine.config the childNode <add name="MySQL Data Provider" invariant="MySql.Data.MySqlClient" and normally you put the same manually in your web.config file. So at the compiling time, when web.config heritates maching.config, it results in duplicate "add" child with the same invariant attribute, with the value "MySql.Data.MySqlClient" .

The examples of use around Internet and the tutorials of ELContrib Application Data Block add the DbProviderFactories node to System.Data element. It suposes that the MySQL .NET/Connector aren't installed in system. It suposes the is referenced in any directory and the configuration isn't heritated from machine.config

Using the code 

Your XML block must be like this to solve the problem: 

    <remove invariant="MySql.Data.MySqlClient"></remove>
    <add name="MySQL Data Provider" invariant="MySql.Data.MySqlClient" description=".Net Framework Data Provider for MySQL" type="MySql.Data.MySqlClient.MySqlClientFactory, MySql.Data, Version=, Culture=neutral" />

Remember to add <remove invariant="MySql.Data.MySqlClient"></remove> at the start of DbProviderFactories.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

AlbertoLeon CSharpMan
Technical Lead Get Me An Apartment
Spain Spain
I'm developer fall in love with C#, .NET and Mono.
Designing and programming websites since 2001.
I like literature (to read and to write), playing football (soccer)... and of course I'm great fan of La Roja (Spain football team)

At now I work in GetMeAnApartment, I do Research and Development features to upgrade our website (, MVC, MySQL) and business model (rental short stay apartments)

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SOFTWARE: Visual Studio 2010, 2008. Monodevelop. Glade. Illustrator. Indesign. Photoshop. Dreamweaver.


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Comments and Discussions

Questionfacing another error Pin
มด ย่อง17-Sep-13 17:30
Memberมด ย่อง17-Sep-13 17:30 
AnswerRe: facing another error Pin
AlbertoLeon CSharpMan17-Sep-13 22:46
MemberAlbertoLeon CSharpMan17-Sep-13 22:46 

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