zero-downtime-05-drop-column

'use strict';
 
const COLUMNS_TO_CHANGE = [
 ['table1',json_col],
 [table2,json_col],
 [table3,json_col],
 [table4,json_col],
];
 
const limit = 2500;
 
function revertRows (Knex, table, json_col, jsonb_col) {
 
 return Knex.raw(`
   UPDATE ${table}
   SET
     ${json_col} = ${jsonb_col}::json
   WHERE id IN (
     SELECT id
     FROM ${table}
     WHERE ${json_col} IS NULL
     AND ${jsonb_col} is NOT NULL
     LIMIT ${limit}
   )
 `)
}
 
exports.up = async (Knex) => {
 
 for (const tableColumnPair of COLUMNS_TO_CHANGE) {
   await Knex.schema.table(tableColumnPair[0], (table) => {
     table.dropColumn(tableColumnPair[1]);
   });
   await Knex.schema.table(tableColumnPair[0], (table) => {
     table.renameColumn(tableColumnPair[1] + '_jsonb', tableColumnPair[1]);
   });
 }
}
 
exports.down = async (Knex) => {
 
 for (const tableColumnPair of COLUMNS_TO_CHANGE) {
   await Knex.schema.table(tableColumnPair[0], (table) => {
     table.renameColumn(tableColumnPair[1], tableColumnPair[1] + '_jsonb');
   });
   await Knex.schema.table(tableColumnPair[0], (table) => {
     table.json(tableColumnPair[1]);
   });
 }
 
 for (const tableColumnPair of COLUMNS_TO_CHANGE) {
   let rowCount = limit;
   do {
     let response = await revertRows(Knex, tableColumnPair[0], tableColumnPair[1], tableColumnPair[1] + '_jsonb');
     rowCount = response.rowCount;
   } while (rowCount === limit)
 }
}
exports.config = {
 transaction: true
}