Microsoft Database Project - 如何更改列类型并避免数据丢失错误

Question

I am trying to change the type of a column from VARCHAR to INT . During the deployment, the database project will stop the deployment due to the "data loss" error:

RAISERROR (N'Rows were detected. The schema update is terminating because data loss might occur.', 16, 127)

I know the data is convertible and if I run a manual ALTER TABLE script it will be fine. However, I cannot integrate that properly with this scenario to avoid the error during the deployment.

1. What is your solution to resolve my problem?
2. Is there a method to override this behaviour in a database project and for this particular case, use a custom script?

Answer 1

One way in such scenario is using PreDeployment script and deploy twice.

1. Change data type column in table definition as usual

2. Add in Predeploy script:

    -- this script has to be idempotent, and removed after some time IF EXISTS (SELECT 1 FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'table_name' AND TABLE_SCHEMA = 'schema_name' AND COLUMN_NAME = 'column_name AND DATA_TYPE.= 'INT' ) BEGIN ALTER TABLE schema_name;table_name ALTER COLUMN Column_name INT NULL/NOT NULL;  END

First publish will change the data type during PreDeploy, and deploy will fail with Potential Data loss error.

Second publish will omit the part of PreDeploy(if condition), and schema compare does not detect any changes, meaning it has been changed.

Next step should be removing the manual part from PreDeployment script.