Entity Framework Migration Best Practices

1.     Introduction

Like code is flown into version control system our database scripts will also be flown into the version control system and upgrading and downgrading the system should be straightforward.

Before starting the Migration:

Every developer should have their own local database for development. They can’t use the shared database for development.

-         Steps for Migration

  1. Enable Migration
    1. This is one-time activity per team. Mostly the team lead when setting up the project will be doing this process.
  1. Add-Migration
    1. For every new migration activity, we will be using this command to start the migration.
  1. Update-Migration
    1. After the changes are done and the changes are ready to push to the database. We will use this Update-Migration to push the changes to the database.

2.     Workflow

When using migration for a single person it will seem less and easy to use and works as expected. If multiple persons are involved then we need to follow some workflow across the team to make it unique.

a.      Spot Check
b.      Craft Migration

Spot Check

When the developer is changing the model, we need to manually check the migration file to see if the desired changes are added to the file. Mainly we need to check the parameters of the individual items.

All String type needs to be validated in the spot check for sure.

Example:
Nullable : false (default to true)
Identiry : true (default to false)
maxLength : n(default to nvarchar(max)) This is very important we need to mention the size explicitly.

Steps to follow for the migration:
  1. Model Change
  2. Add-Migration
  3. Spot Check
  4. Any issue Delete Migration and start Step 1
  5. If no issue then Update Database
Handling the Conflicts for Rebase workflow Approach:

  1. Person A Follows the above process to commit it to Git
  2. Person B also does the changes in the same file (model) and trying the above steps
  3. When Person B Pull the changes from Master (where Person A Committed), Person B branch will get conflict
  4. Follow the steps to resolve the conflict

  1. Rebase the branch -> Git Rebase - -abort
  2. Go to VS and point to the Migration where we were before the changes, in respect to the Migration.  Update-Database –TargetMigration <<MigrationName>>
  3. Delete the migration which we added and end up having the conflict
  4. Now the models are changed and there is no Migration for it
  5. Commit the changes (Migration file will be removed from the solution)
  6. Squash the second to the first <<need more details>>
  7. (Feature Branch -> Target Migration -> Squash)

Handling the Conflicts for Merge Workflow Approach:

When we get the latest from the source control and we end up with conflict. Steps to resolve the conflict...

  1. Resolve the conflict file by file (normal merge process)
  2. And after resolving the conflicts, we need to Merge Migration.
    1. Add-Migration –IgnoreChanges <<MigrationName>>
    2. Update-Database
  3. Empty migration will be created with no Up and Down items.
  4. This step is to update the metadata in the database where we have the binary of the models.
  5. (Merge Migration -> Simpler, but not as Clean)
  6. End up having multiple empty migrations
Tips:

Update-Database –TargetMigration <<MigrationName>>

If Conflict Then,
Git rebase –abort

Whenever we are adding a column to the existing table then that column should be Nullable (why we can’t have a Default value tied to it for existing data??)

Enum -> Seed

Look Up -> Custom Migration

Complex Lookup - > temp taple + use it to insert it.

Whenever a Column/Table is renamed the Migration will drop and recreate it. Instead, when we spot check it we need to change it to Rename instead of Drop and recreate.

Always test Up and Down method for each migration.

If you want to see what scripts are running by the entity framework then use –Verbose.

To avoid the empty Up and Down Migration, we can use the Add-Migration <<MigrationName>> -Ignorechanges

Update-Database –TargetMigration: <name of last good migration>

Testing Steps

-          If the Migration applied already to the database is Migration12
-          Now we are introducing the Migration13 with Up and Down Methods
-          To Test the Up Method we will use Update database and see whether it is failing

-          To test the Down method for Migration13

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