TransactionScope and SQLite database gets locked

Question

I am trying to use Entity Framework 6 with SQLite and running into a database locked issue when trying to use TransactionScope. Here is my code:

using (var txn = new TransactionScope())
{
    using (var ctx = new CalibreContext())
    {
        var book = ctx.Books.First(x => x.Id == 2);
        var author = ctx.Authors.First(x => x.Id == 3);
        book.Authors.Add(author);
        ctx.SaveChanges();
    }
    txn.Complete();
}

First line var book = ctx.Books.First(x => x.Id == 2); executes ok. but then once I move on to the next one I get an exception saying that my database is locked. Here is my app config:

<configuration>
  <configSections>
    <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
    <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
  </configSections>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0" />
  </startup>
  <connectionStrings>
    <add name="CalibreContext" connectionString="Data Source=metadata.db" providerName="System.Data.SQLite.EF6" />
  </connectionStrings>
  <system.data>
    <DbProviderFactories>
      <remove invariant="System.Data.SQLite" />
      <add name="SQLite Data Provider" invariant="System.Data.SQLite" description=".Net Framework Data Provider for SQLite" type="System.Data.SQLite.SQLiteFactory, System.Data.SQLite, Version=1.0.98.0, Culture=neutral, PublicKeyToken=db937bc2d44ff139" />
      <remove invariant="System.Data.SQLite.EF6" />
      <add name="SQLite Data Provider (Entity Framework 6)" invariant="System.Data.SQLite.EF6" description=".Net Framework Data Provider for SQLite (Entity Framework 6)" type="System.Data.SQLite.EF6.SQLiteProviderFactory, System.Data.SQLite.EF6, Version=1.0.98.0, Culture=neutral, PublicKeyToken=db937bc2d44ff139" />
    </DbProviderFactories>
  </system.data>
  <entityFramework>
    <defaultConnectionFactory type="Calibre.Dal.Ef.SQLiteConnectionFactory, Calibre.Dal.Ef" />
    <providers>
      <provider invariantName="System.Data.SQLite.EF6" type="System.Data.SQLite.EF6.SQLiteProviderServices, System.Data.SQLite.EF6, Version=1.0.98.0, Culture=neutral, PublicKeyToken=db937bc2d44ff139" />
      <provider invariantName="System.Data.SQLite" type="System.Data.SQLite.EF6.SQLiteProviderServices, System.Data.SQLite.EF6, Version=1.0.98.0, Culture=neutral, PublicKeyToken=db937bc2d44ff139" />
    </providers>
  </entityFramework>
</configuration>

I need to use TransactionScope because in addition to performing a DB operation, I also have to perform a file system operation that I plan on adding to the same transaction (currently not there).

Answer 1

I was experiencing a similar issue. Just to be clear, the error I got on the second query was "the underlying provider failed on Open" (but the reason for the Open failure was that the database was locked).

Apparently the issue is related to MSDTC (TransactionScope is tightly coupled to MSDTC).

I found a community addition to an MSDN page which in turn references this blog post
... which states that transactions are "promoted" to MSDTC transactions if a connection is closed and reopened. Which EF does by default. Normally this is a good thing -- you don't want database handles hanging around forever -- but in this case that behavior gets in the way.

The solution is to explicitly open the database connection:

using (var txn = new TransactionScope())
{
    using (var ctx = new CalibreContext())
    {
        ctx.Connection.Open();
        // ... remainder as before ...

Alternatively, if all your CalibreContext objects are short-lived, you could conceivably open the connection in the CalibreContext constructor.

This seems to have fixed my issue. I'll post an update if I have anything else to report.

Answer 2

One common situation to cause this problem is that another application is accessing the same database.

In my situation it’s because that I opened the database with DB Browser for SQLite, deleted a database table and not applying the changes.

Clicking Write Changes (or Revert Changes or Close Database) and the error will be gone.

(Taken from http://redino.net/blog/2017/03/net-sqlite-database-locked)