问题
Is it possible to transform data stored in a column using a calculation performed in c# during an Entity First database migration?
Currently, I have a column named Content of type nvarchar. I'd like to replace it with a column named ContentBinary of type varbinary, copying the content of each row in the process, but also transforming the content.
Specifically, I want to convert the string to a UTF-8 encoding and then compress it.
I know that the DbMigration class allows for transformation / data motion using the Sql*() methods, but those methods appear to require all the transformation logic to be in SQL. I think that would require the compression logic to be duplicated as a stored procedure in SQL Server, which would double the effort required and lead to the potential for inconsistencies over just using the custom c# compression routine directly.
I'd like to be able to iterate through all the rows, read each Content value, apply the transformation in C#, and then write it to ContentBinary.
I think this may need to happen as part of the migration transaction for consistency but also because only Content will exist before the migration and only ContentBinary will exist afterward. I assume that rules out opening a separate database connection during the migration. However, if there is a way to access the connection being used for the migration transaction, perhaps that would be enough.
回答1:
you can use the AddOrUpdate method like the following
context.TableName.AddOrUpdate(x=> x.ID, collection);
where the collection is the table itself after apply transforming
if you provided some code in your question may be I could be more specific.
来源：https://stackoverflow.com/questions/34969076/transform-data-using-c-sharp-during-entity-framework-migration