无法在实体框架中生成显式迁移

It tells you that there is some unprocessed migration in your application and it requires running Update-Database before you can add another migration.

You either need to run "update-database" from the package manager console to push your changes to the database OR you can delete the pending migration file ([201203170856167_left]) from your Migrations folder and then re-run "add-migration" to create a brand new migration based off of your edits.

If you haven't used Update-Database you can just delete it. If you've run the update then roll it back using Update-Database -TargetMigration "NameOfPreviousMigration", then delete it.

Reference: http://elegantcode.com/2012/04/12/entity-framework-migrations-tips/

I copied this text directly from here: How do I undo the last Add-Migration command?

I had the same problem. Apparently entity framework generates this error when it's unable to connect to the database. So make sure that you're able to access it before searching for other problems.

This error can also mean that the migrations are not recognized anymore. This happened to me after having changed the value of the ContextKey in Migrations.Configuration. The solution was simply to update the ContextKey in the database table "__MigrationHistory" (or revert the value in the Configuration class I guess). The ContextKey and the Namespace in your application should match.

When running into this issue, please try adding parameters to your add-migration cmdlet. For example, specifying the start up project as well as the connection string name could help EF find your target database.

add-migration Delta_Defect_0973 -ConfigurationTypeName your.namespace.ContextClassName -StartUpProject DeltaProject -ConnectionStringName DeltaSQL

Where:

Delta_Defect_0973 is the name of your migration

your.namespace.ContextClassName is the name of your Configuration class in your migration folder, prefixed with the full name space.

DeltaProject is the name of your main project with your web.config or app.config file.

DeltaSQL is the name of your connection string defined in your web.config or app.config file.

1. Connection String / Connection Permissions

Check the connection string again.

Make sure the user you are connecting with still has permission to read from [__MigrationHistory] and has permission to edit the schema.

You can also try changing the connection string in the App or Web config file to use Integrated Security (Windows Auth) to run the add-migration command as yourself.

For example:

connectionString="data source=server;initial catalog=db;persist security info=True;Integrated Security=SSPI;"

This connection string would go in the App.config file of the project where the DbContext is located.

2. StartUp Project

You can specify the StartUp project on the command line or you can right click the project with the DbContext, Configuration and Migrations folder and select Set as StartUp project. I'm serious, this can actually help.

Scenario

• I am working in a branch in which I created a new DB migration.
• I am ready to update from master, but master has a recent DB migration, too.
• I delete my branch's db migration to prevent conflicts.
• I "update from master".

Problem

After updating from master, I run "Add-Migration my_migration_name", but get the following error:

Unable to generate an explicit migration because the following explicit migrations are pending: [201607181944091_AddExternalEmailActivity]. Apply the pending explicit migrations before attempting to generate a new explicit migration.

So, I run "Update-Database" and get the following error:

Unable to update database to match the current model because there are pending changes and automatic migration is disabled

Solution

At this point re-running "Add-Migration my_migration_name" solved my problem. My theory is that running "Update-Database" got everything in the state it needed to be in order for "Add-Migration" to work.

This error means there are pending migrations need to be commited before you can execute another explicit migration. You can choose to

1. Execute those pending migrations using Update-Database command
2. Delete those pending migrations. Safest way is open Migrations folder, right click on [201203170856167_left] > Exclude from project

After this one you can start "Add-Migration ..." again

Hope it helps

I also came across this issue. It came when I created new DB and I had pending changes for my code-first DB migration then I tried to run "Update-Database" command. Solution : Run "Add-Migration -MigrationName" command to create new migration for new DB. Then run "Update-Database" command.

I had the same problems and was only able to resolve it running Add-Migration 'MigrationName' -Force

With -Force being the important part.

I had this problem too for a database that I knew was up to date when running Add-Migration. Solved by simply running the Add-Migration command a second time. Suspect a connectivity issue, as suggested by Robin Dorbell above.

Had the same issue and was able to solve with some hints from above answers:

• In package manager console check the default project (point to the project with the migration configuration
• Ensure the startup-proj has a web.config with a valid connectionstring ( or
• Ensure the project with migrations has an app.config / web.config with a valid connectionstring
• Check permissions in DB (for the user configured in you connectionstring)

Use "update-database -verbose" in the package manager console to get more specific information where migrations tries to connect to. (Helped in my case to find out my startup proj was not set correctly...)

Just my two cents:

My scenario:

1. I restored my local database to a working state.
2. Already had migrations already applied to it.
3. Whenever I tried adding a new migration i got the error about pending migrations as mentioned my the OP.

Solution:

To get around this i just provided more explicit parameters:

Add-Migration -ConnectionString "Server=localhost\SQLEXPRESS;Database=YourDataBase;Trusted_Connection=True;" -ConnectionProviderName "System.Data.SqlClient" -verbose

I am lead to believe that you can set a setting in your app.config folder to allow you to default this behaviour so you don't have to provide explicit parameters everytime. However I am not sure on how to do this.

That was happened when i suddenly renamed class of old migration that already exist in db. I checked VCS history, determined that and renamed back. All worked afterwards.

My local database did not have the __MigrationHistory populated, or existing. I manually created the table, and then migrated the data in that table from PROD to my local database. This caused VS to think the migrations had been applied (which they had been).

I suffered exactly the same problem just after reverting from a migration to another.

In my case I "targetedmigration" from "migration06" to "migration04".

I needed to delete the "migration0"6 and then I was able to force creating the "migration05". This basically means that you need to just keep the next migration after the targeted one.

Tip: It's always good to use the -Script switch for migration commands if you're not sure. It also really helps understand what Update-Database actually does.

I run the following to update the database, then I get a script I can apply manually (or just run it again without the -Script tag).

For Update-Database I would run the following :

Update-Database -Script -ConfigurationTypeName Configuration_ASPNETIdentity -ConnectionStringName SQL_AzureLive

Where SQL_AzureLive is the named connection string in my config.

Then I can verify the SQL looks right, apply it and be done. As many others have said if the connection string is wrong or invalid you'll get this error.

There is an ambiguity and so error. Best way is to exclude the current migration file and create new migration(add-migration) file and then copy the content of new migration to excluded file and include it again and run update-database command.

I did another way. I droped database entirely and run "update-database" again in vs.

I had a simpler problem. VS erroneously reported this error when I had a VPN connection to a client's site connected on my workstation. The problem was that the DBMS security was set to accept requests only from my real local IP. Simply turning off the VPN resolved the problem.

i solved same problem like this:

• delete old migration file
• update-database -force
• Add-Migration AddedEntity
• update-database

In my case (using MS Visual Studio), it was as simple as restarting Visual Studio.

For me, i deleted the migration file(in your case "201203170856167_left") from Migrations folder, and then ran the below command in Package Manager console

Add-Migration <Parameter>
Update-Database

In my case, I forgot to add my IP address in firewall rules in Azure, basically as I was unable to connect to the database I was getting this error. So specifically for my case, I added my IP address in database firewall rules in Azure and it all worked well. Apart from this, it could be the issue of proxy/internet connection/DB username password/DB connection string etc. OR obviously, you might have pending migrations for which you need to run Update-Database command.

Historically I always solved this by deleting the pending migrations, or if there was only 1 remaining and it was mostly desirable, by using -f to recreate it.

Recently, this has stopped working for me.

When this happened the first time, I restarted Visual Studio, and then it let me proceed.

The second time, it only worked after I ran a Clean on the project. It was almost as if the pending migrations were retained despite deleting all the files from explorer.

This isn't going to be the answer for many people, but EF will chuck this error when it can't connect to the DB. If you're working from home like I am, make sure you're still connected to your VPN!

Old post but might help someone. For me it happened because I renamed Assembly name and Default namespace of the project. So I had to update ContextKey in _MigrationHisotry table to the new value of Assembly name or Default namespace. Honestly I don't know which one should be used, because for me both are same!

In my case, just changed the startup project to the one that contains my migrations folder, also make sure that you selected the same project in the package console manager.

You just have to update your database use this command in the NuGet package manager console. update-database

I've just seen this and it was because the SQL login account (used in the connection string) had 'Enforce password expiration' set in SQL Server Management Studio, and the password had expired! Hence it couldn't connect to the database to see existing migrations!