Liquibase preconditions: How do I check for a column being non-nullable?

问题

I have a db upgrade script to remove the non-null constraint on a column. I want to do a precondition check, and call ALTER TABLE only when it is non-null.

The master.xml script is a progressive one where I keep adding scripts and the entire thing runs everytime. After the first time my Alter Table script has run, I do not want it to be run again.

Couldn't find a predefined precondition for this, and could not write an sqlcheck either.

回答1:

Can be done with sqlCheck.

For MySql

<preConditions onFail="MARK_RAN" onError="CONTINUE">
    <sqlCheck expectedResult="NO">
        SELECT is_Nullable
        FROM  INFORMATION_SCHEMA.COLUMNS 
        WHERE table_name='<table_name>' 
        AND column_name='<column_name>' 
    </sqlCheck>   
</preConditions>

For Oracle:

<preConditions onFail="MARK_RAN" onError="CONTINUE">
    <sqlCheck expectedResult="N">
        SELECT Nullable
        FROM user_tab_columns
        WHERE table_name = '<table_name>'
        AND column_name = '<column_name>'
    </sqlCheck>
</preConditions>

For SQL Server:

<preConditions onFail="MARK_RAN" onError="CONTINUE">
    <sqlCheck expectedResult="0">
      SELECT is_nullable 
      FROM sys.columns
      WHERE  object_id = OBJECT_ID('<table_name>')  
      AND name = '<column_name>' 
    </sqlCheck>
</preConditions>

回答2:

Revising my answer. Liquibase supports an add not null constraint operation as follows:

<changeSet author="me" id="example-001">
    <addNotNullConstraint 
        tableName="mytable"    
        columnName="mycol"
        columnDataType="VARCHAR(10)"
        defaultNullValue="NULL"/>
</changeSet>

This automatically handles columns that are null, in my example populating them with the text string "NULL".

I don't think this changeset requires a pre-condition. Worst case you'd re-apply the existing column constraint, once. Liquibase tracks all changsets and ensures they are not executed again.

来源：https://stackoverflow.com/questions/17746031/liquibase-preconditions-how-do-i-check-for-a-column-being-non-nullable

标签

mysql

liquibase

preconditions