EF data migration, the object reference is not set to the object instance, ef instance

EF data migration, the object reference is not set to the object instance, ef instance

Symptom:

When you execute Enable-Migrations-force, the following error occurs:

DbProviderServicesExtensions. GetProviderManifestTokenChecked

 

 

Cause:

1. The entityFramework node or connectionStrings node is not configured in App. config or web. config of the project startup Item. EF cannot find the database connection string information during data migration.

2. The project startup Item configuration is incorrect. You should select a project with an entityFramework node or connectionStrings node as the startup project.