Gorm Scopes that use subqueries generate invalid SQL

GORM Playground Link

https://github.com/go-gorm/playground/pull/431

Description

When using a scope that defines a subquery, Gorm generates invalid SQL that fails to execute. For example, in the provided playground, the generated SQL misses a table name and has unbalanced parentheses:

SELECT * FROM (SELECT * FROM () AS sub WHEREsub.deleted_atIS NULL

This does no happen when the scope avoids using its provided *gorm.DB to define the model to work with, and instead uses a global *gorm.DB.

Investigation

While digging into the issue, I found that the *gorm.DB that the scope returns has a Statement.TableExpr *clause.Expr which Vars []interface{} contains another *gorm.DB. That *gorm.DB itself has a Statement.TableExpr that points to the same clause.Expr.

This looks like an abnormal circular reference, which Gorm seems to handle by generating incomplete SQL rather than an infinite loop.

Comment From: li-jin-gou

please refer to this document https://gorm.cn/docs/method_chaining.html @ortolot