{"id":135685,"date":"2019-10-03T04:16:36","date_gmt":"2019-10-03T04:16:36","guid":{"rendered":"https:\/\/inchoo.net\/?p=35423"},"modified":"2019-10-03T04:16:36","modified_gmt":"2019-10-03T04:16:36","slug":"declarative-schema-feature-in-magento-2","status":"publish","type":"post","link":"https:\/\/www.sushilkumar.ind.in\/blog\/magento-2\/declarative-schema-feature-in-magento-2\/","title":{"rendered":"Declarative Schema feature in Magento 2"},"content":{"rendered":"

First of all, what is declarative schema in Magento 2? It is a new way of working with database without developers having to write various scripts for each new module version. It was introduced in 2018 with Magento 2.3 and it’s one of the major changes. In this article you will learn how to use declarative schema and apply data patches.<\/span><\/p>\n

Why declarative schema?<\/h2>\n

What are the advantages of using declarative schema? In short, before it, we had to write database scripts in PHP which is not a perfect solution. That’s because when you upgrade Magento to a version several releases ahead of the installed version, all the upgrade scripts between those two versions will still be executed. In other words, this creates unnecessarily complex situations. The new approach allows us to declare the final state of the database and the system automatically adjusts to it. Furthermore, when you uninstall the module, data will be deleted.<\/p>\n

Declarative Schema Configuration<\/h2>\n

Let’s say you have a module with version 1.0.0 and the latest version is 1.0.3. When you upgrade it, script changes for 1.0.1 and 1.0.2 will also be applied. This is less than ideal because Magento applies changes blindly. What that means is that in one version you might introduce a column and then delete it in the very next. That’s one of the problems declarative schema eliminates. Using it, Magento determines the differences between the current table structure and what it should look like.<\/p>\n

You’ll have to create a new module<\/a> before we dig into working with database.<\/p>\n

In the Module\/etc\/ folder create db_schema.xml. This is the file where you will define your tables, columns, pretty much everything you need. I made a simple example with two tables to show you how to do it.<\/p>\n

<?xml<\/span> version<\/span>="1.0"<\/span>?><\/span><\/span>\n<schema<\/span> xmlns:xsi<\/span>="http:\/\/www.w3.org\/2001\/XMLSchema-instance"<\/span><\/span>\n xsi:noNamespaceSchemaLocation<\/span>="urn:magento:framework:Setup\/Declaration\/Schema\/etc\/schema.xsd"<\/span>><\/span><\/span> <table<\/span> name<\/span>="inchoo_declarative_schema1"<\/span> resource<\/span>="default"<\/span> engine<\/span>="innodb"<\/span> comment<\/span>="Inchoo Table 1"<\/span>><\/span><\/span> <column<\/span> xsi:type<\/span>="int"<\/span> name<\/span>="table_1_id"<\/span> padding<\/span>="10"<\/span> unsigned<\/span>="true"<\/span> nullable<\/span>="false"<\/span> identity<\/span>="true"<\/span> comment<\/span>="ID"<\/span>\/><\/span><\/span> <column<\/span> xsi:type<\/span>="varchar"<\/span> name<\/span>="name"<\/span> comment<\/span>="Name"<\/span>\/><\/span><\/span> <constraint<\/span> xsi:type<\/span>="primary"<\/span> referenceId<\/span>="PRIMARY"<\/span>><\/span><\/span> <column<\/span> name<\/span>="table_1_id"<\/span>\/><\/span><\/span> <\/constraint><\/span><\/span><\/span> <\/table><\/span><\/span><\/span> <table<\/span> name<\/span>="inchoo_declarative_schema2"<\/span> resource<\/span>="default"<\/span> engine<\/span>="innodb"<\/span> comment<\/span>="Inchoo Table 2"<\/span>><\/span><\/span> <column<\/span> xsi:type<\/span>="int"<\/span> name<\/span>="table_2_id"<\/span> padding<\/span>="10"<\/span> unsigned<\/span>="true"<\/span> nullable<\/span>="false"<\/span> identity<\/span>="true"<\/span> comment<\/span>="ID"<\/span>\/><\/span><\/span> <column<\/span> xsi:type<\/span>="text"<\/span> name<\/span>="content"<\/span> comment<\/span>="Content"<\/span>\/><\/span><\/span> <constraint<\/span> xsi:type<\/span>="primary"<\/span> referenceId<\/span>="PRIMARY"<\/span>><\/span><\/span> <column<\/span> name<\/span>="table_2_id"<\/span>\/><\/span><\/span> <\/constraint><\/span><\/span><\/span> <\/table><\/span><\/span><\/span>\n<\/schema><\/span><\/span><\/span><\/code><\/pre>\n
Running setup:upgrade will create two tables, inchoo_declarative_schema1 and inchoo_declarative_schema2 with IDs and an additional column. As you can see, the ID columns are set as primary key.<\/p>\n
Tables<\/h4>\n
The table node can contain three different types of subnodes:<\/p>\n