feat: expose knex query builder instance in schema classes

Schema builder queries are directly handled by Knex and therefore schema
properties that needs access to the query builder should use the knex
query builder

Closes: #832

adonis-typings/schema.ts

@@ -34,6 +34,7 @@ declare module '@ioc:Adonis/Lucid/Schema' {
     db: QueryClientContract
     schema: Knex.SchemaBuilder
     now(precision?: number): Knex.Raw
+    knex(): Knex.QueryBuilder
     raw(sql: string, bindings?: RawQueryBindings): Knex.Raw
     defer: (cb: DeferCallback) => void
     up(): Promise<void> | void

src/Schema/index.ts

@@ -125,6 +125,13 @@ export class Schema implements SchemaContract {
     return this.db.knexRawQuery(query, bindings)
   }
 
+  /**
+   * Get access to the underlying knex query builder
+   */
+  public knex() {
+    return this.db.knexQuery()
+  }
+
   /**
    * Wrapping database calls inside defer ensures that they run
    * in the right order and also they won't be executed when

test/migrations/schema.spec.ts

@@ -350,4 +350,36 @@ test.group('Schema', (group) => {
     await db.connection().schema.dropTable('schema_accounts')
     await db.connection().schema.dropTable('schema_users')
   })
+
+  test('define index predicate as knex query', async ({ assert }) => {
+    class UsersSchema extends getBaseSchema() {
+      public up() {
+        this.schema.createTable('users', (table) => {
+          table.increments('id')
+          table.index(['name', 'last_name'], 'idx_name_last_name', {
+            indexType: 'FULLTEXT',
+            storageEngineIndexType: 'hash',
+            predicate: this.knex().whereNotNull('email'),
+          })
+        })
+      }
+    }
+
+    const schema = new UsersSchema(db.connection(), 'users.ts', true)
+    const queries = await schema.execUp()
+
+    const knexSchema = db
+      .connection()
+      .schema.createTable('users', (table) => {
+        table.increments('id')
+        table.index(['name', 'last_name'], 'idx_name_last_name', {
+          indexType: 'FULLTEXT',
+          storageEngineIndexType: 'hash',
+          predicate: db.connection().knexQuery().whereNotNull('email'),
+        })
+      })
+      .toQuery()
+
+    assert.deepEqual(queries, [knexSchema])
+  })
 })