How to drop a column from the table using the db.schema.xml file in Magento 2?

December 28, 2023
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How to drop a column from the table using the db.schema.xml file in Magento 2 – We all know from Magento 2.3 that Declarative Schema (db.schema.xml) was introduced to create the database tables in Magento 2. After creating a table and developing the custom extension you may feel free to drop/remove unwantedly created columns. To drop a column you can do it using the same db.schema.xml file.

I have noticed a question related to this topic in AD0-E717 Adobe Commerce

Developer with Cloud Add-on Professional exam.

Question – What should be done to allow the removal of columns from the database when deleting them from db.schema.xml?

  • A. The removable columns should be defined in db_schema_whitelist.json.
  • B. The columns should have “removable” attribute set to “true” in the db.schema.xml.
  • C. The removable columns should be defined in db.schema_blacklist.json.

So to check the answer practically I tried, What I found was to remove a column using db.schema.xml, and add disabled=true to the relevant column. After that need to update the db_schema_whitelist.json file.

For example, let’s say you have added a column like this

<column name="answer" nullable="true" xsi:type="text" comment="answer"/>

You need to update this column line below

<column name="answer" nullable="true" xsi:type="text" comment="answer"  disable="true"/>

After this need to update the db_schema_whitelist.json as follows and generate the db_schema_whitelist.json file.

{
    "ayakil_faq_faq": {
        "column": {
            "answer": true,
        },
        "constraint": {
            "PRIMARY": true
        }
    }
}

To generate the db_schema_whitelist.json file. you need to run the below command.

bin/magento setup:db-declaration:generate-whitelist --module-name=YourModule_Name

After updating the codes you need to run setup:upgrade command. After clear:cache command you can see the field is removed from the table.

So for the above question, I choose Answer A.

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