Ttdfjt

I have follow this documnet https://devdocs.magento.com/guides/v2.3/extension-dev-guide/declarative-schema/db-schema.html but not get success

module.xml

 <?xml version="1.0"?>
 <!--
 /**
 * Copyright © Krish TechnoLabs, All rights reserved.
 */
 -->
 <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
 <module name="Ktpl_Test1" setup_version="1.0.0">
 <sequence>
 <module name="Magento_Eav"/>
 </sequence>
 </module>
 </config>

db_schema.xml

 <?xml version="1.0"?>
 <!--
 /*
 * Copyright © 2019 Krish Technolabs. All rights reserved.
 * See COPYING.txt for license details
 */
 -->
 <schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
 <table comment="Test Table 1" engine="innodb" name="ktpl_test1" resource="default">
 <column identity="true" name="test1_id" nullable="false" padding="10" unsigned="true" xsi:type="int"/>
 <column name="test_name" nullable="false" padding="10" unsigned="true" xsi:type="int"/>
 <column name="test2_id" nullable="false" padding="10" unsigned="true" xsi:type="int"/>
 <constraint referenceId="PRIMARY" xsi:type="primary">
 <column name="test1_id"/>
 </constraint>
 <constraint xsi:type="foreign" referenceId="Test12ID" table="ktpl_test1" column="test2_id" referenceTable ="ktpl_test2" referenceColumn="test2_id"/>
 <constraint xsi:type="foreign" referenceId="Test13ID" table="ktpl_test1" column="test3_id" referenceTable ="ktpl_test3" referenceColumn="test3_id"/>
 </table>
 <table name="eav_attribute" resource="default" engine="innodb" comment="Eav Attribute">
 <column xsi:type="mediumtext" name="note" nullable="false" length="500" comment="Note"/>
 <constraint xsi:type="primary" referenceId="PRIMARY">
 <column name="attribute_id"/>
 </constraint>
 </table>
 </schema>

The only mistake you are doing here is length attribute, just remove it.

This is the working code..

etcdb_schema.xml

<?xml version="1.0"?>

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
 <table name="eav_attribute" resource="default" engine="innodb" comment="Eav Attribute">
 <column xsi:type="mediumtext" name="note" nullable="true" comment="Note"/>
 </table>
</schema>

Create db_schema.xml file in your module and add this below code :

app/code/VendorName/ModuleName/etc/db_schema.xml

<schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Setup/Declaration/Schema/etc/schema.xsd">
 <table name="eav_attribute">
 <column xsi:type="mediumtext" name="note" nullable="true" length="255" comment="Note"/>
 <constraint xsi:type="primary" referenceId="PRIMARY">
 <column name="attribute_id"/>
 </constraint>
 </table>
</schema>

Now, execute this below command in your Magento root directory

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

Make sure, there are db_whitelist_schema.json file will be create in app/code/VendorName/ModuleName/etc folder.

Now, upgrade, deploy and clean cache

php bin/magento s:up
php bin/magento s:s:d -f
php bin/magento c:c

Hope, it will helpful for you.

UPDATE :

de_whitelist_schema.json (After install ktpl_test1 table) :

 "ktpl_test1": 
 "column": 
 "test1_id": true,
 "test_name": true,
 "test2_id": true
 ,
 "constraint": 
 "PRIMARY": true
 
 ,
 "eav_attribute": 
 "column": 
 "note": true
 ,
 "constraint": 
 "PRIMARY": true