Entity First：schema sync

            quote! {
                sea_orm::register_entity! {
                    sea_orm::EntityRegistry {
                        module_path: module_path!(),
                        schema_info: |schema| sea_orm::EntitySchemaInfo::new(Entity, schema),
                    }
                }
            }

        let mut prefix = prefix.trim_end_matches("*");
        if !prefix.contains("::") {
            string = format!("{prefix}::");
            prefix = &string;
        }
        if let Some((left, right)) = prefix.split_once("::") {
            if left.contains("-") {
                // convert crate name to module path
                let left = left.replace('-', "_");
                string = format!("{left}::{right}");
                prefix = &string;
            }
        }
        debug!("Registering entities with prefix `{prefix}`");
        for entity in inventory::iter::<crate::EntityRegistry>() {
            if entity.module_path.starts_with(prefix) {
                schema.register_entity((entity.schema_info)(schema.helper()));

--- e1 with prefix "sync_more::e1::t" (no ::*)
  wire> CREATE TYPE "t_status" AS ENUM ('draft', 'done')
  wire> CREATE TABLE "t" ( "id" integer GENERATED BY DEFAULT AS IDENTITY NOT NULL PRIMARY KEY, "status" t_status NOT NULL )
  wire> CREATE TABLE "t_extra" ( "id" integer GENERATED BY DEFAULT AS IDENTITY NOT NULL PRIMARY KEY )
  sync => Ok(())
  tables in so_mig_sync: ["t", "t_extra"]

        let mut sorter = TopologicalSort::<TableName>::new();

        for entity in self.entities.iter() {
            let table_name = get_table_name(entity.table.get_table_name());
            sorter.insert(table_name);
        }
        for entity in self.entities.iter() {
            let self_table = get_table_name(entity.table.get_table_name());
            for fk in entity.table.get_foreign_key_create_stmts().iter() {
                let fk = fk.get_foreign_key();
                let ref_table = get_table_name(fk.get_ref_table());
                if self_table != ref_table {
                    // self cycle is okay
                    sorter.add_dependency(ref_table, self_table.clone());
                }
            }
        }
        let mut sorted = Vec::new();
        while let Some(i) = sorter.pop() {
            sorted.push(i);
        }
        if sorted.len() != self.entities.len() {
            // push leftover tables
            for entity in self.entities.iter() {
                let table_name = get_table_name(entity.table.get_table_name());
                if !sorted.contains(&table_name) {
                    sorted.push(table_name);
                }
            }
        }

--- cycle a <-> b on an empty schema
  wire> CREATE TABLE "b" ( "id" integer GENERATED BY DEFAULT AS IDENTITY NOT NULL PRIMARY KEY, "a_id" integer, CONSTRAINT "fk-b-a_id" FOREIGN KEY ("a_id") REFERENCES "a" ("id") )
  wire< ErrorResponse 42P01 relation "a" does not exist
  sync => Err("Execution Error: error returned from database: relation \"a\" does not exist at line 434")
  tables in so_mig_cyc: []
--- cycle again
  wire> CREATE TABLE "b" ( "id" integer GENERATED BY DEFAULT AS IDENTITY NOT NULL PRIMARY KEY, "a_id" integer, CONSTRAINT "fk-b-a_id" FOREIGN KEY ("a_id") REFERENCES "a" ("id") )
  wire< ErrorResponse 42P01 relation "a" does not exist
  sync => Err("Execution Error: error returned from database: relation \"a\" does not exist at line 434")
  tables in so_mig_cyc: []

for (v, what) in steps {
  println!("--- {v}: {what}");
  let before = w.count.load(Ordering::SeqCst);
  w.quiet.store(false, Ordering::SeqCst);
  let r = db.get_schema_registry(&format!("sync_steps::{v}::*")).sync(&db).await;
  settle().await;
  w.quiet.store(true, Ordering::SeqCst);
  let n = w.count.load(Ordering::SeqCst) - before;
  println!("  sync => {:?}, {n} statements in total", r.map_err(|e| e.to_string()));
  // ... 打印 user 的列；v6..v8 再打印 user 上的唯一索引，以及它是不是一个约束
}

--- v1: user + post (post belongs_to user), registry order as inventory yields it
  wire> CREATE TABLE "user" ( "id" integer GENERATED BY DEFAULT AS IDENTITY NOT NULL PRIMARY KEY, "name" varchar NOT NULL, "email" varchar NOT NULL UNIQUE )
  wire> CREATE TABLE "post" ( "id" integer GENERATED BY DEFAULT AS IDENTITY NOT NULL PRIMARY KEY, "user_id" integer NOT NULL, "title" varchar NOT NULL, CONSTRAINT "fk-post-user_id" FOREIGN KEY ("user_id") REFERENCES "user" ("id") )
  sync => Ok(()), 5 statements in total
  user: id integer not null, name character varying not null, email character varying not null
--- v2: user + bio: Option<String>
  wire> ALTER TABLE "user" ADD COLUMN "bio" varchar
  sync => Ok(()), 10 statements in total
  user: id integer not null, name character varying not null, email character varying not null, bio character varying
--- v3: user + nickname: String, the table has one row
  wire> ALTER TABLE "user" ADD COLUMN "nickname" varchar NOT NULL
  wire< ErrorResponse 23502 column "nickname" of relation "user" contains null values
  sync => Err("Execution Error: error returned from database: column \"nickname\" of relation \"user\" contains null values at line 6111"), 10 statements in total
  user: id integer not null, name character varying not null, email character varying not null, bio character varying

--- v4: user.name: String -> i64
schema sync: column `user`.`name` is `varchar` in the database but the entity defines `bigint`; sync is non-destructive and will not alter it (apply the change with a migration)
  sync => Ok(()), 9 statements in total
  user: id integer not null, name character varying not null, email character varying not null, bio character varying

--- v6: user.name gets #[sea_orm(unique)]
  wire> CREATE UNIQUE INDEX IF NOT EXISTS "idx-user-name" ON "user" ("name")
  sync => Ok(()), 10 statements in total
  user: id integer not null, name character varying not null, email character varying not null, bio character varying
  unique indexes on user: idx-user-name (index only), user_email_key (constraint), user_pkey (constraint)
--- v7: user.email loses #[sea_orm(unique)]
  wire> ALTER TABLE "user" DROP CONSTRAINT "user_email_key"
  sync => Ok(()), 10 statements in total
  user: id integer not null, name character varying not null, email character varying not null, bio character varying
  unique indexes on user: idx-user-name (index only), user_pkey (constraint)
--- v8: user.name loses #[sea_orm(unique)]
  wire> ALTER TABLE "user" DROP CONSTRAINT "idx-user-name"
  wire< ErrorResponse 42704 constraint "idx-user-name" of relation "user" does not exist
  sync => Err("Execution Error: error returned from database: constraint \"idx-user-name\" of relation \"user\" does not exist at line 12276"), 10 statements in total
  user: id integer not null, name character varying not null, email character varying not null, bio character varying
  unique indexes on user: idx-user-name (index only), user_pkey (constraint)
--- v8 again (does the failure go away?)
  sync => Err("Execution Error: error returned from database: constraint \"idx-user-name\" of relation \"user\" does not exist at line 12276")
--- fix by hand: DROP INDEX "idx-user-name", then v8 again
  sync => Ok(())

--- v9: name -> full_name, renamed_from = "name"
  wire> ALTER TABLE "user" RENAME COLUMN "name" TO "full_name"
  sync => Ok(()), 10 statements in total
  user: id integer not null, full_name character varying not null, email character varying not null, bio character varying
--- v10: new table comment(id, post_id), no relation
  wire> CREATE TABLE "comment" ( "id" integer GENERATED BY DEFAULT AS IDENTITY NOT NULL PRIMARY KEY, "post_id" integer NOT NULL )
  sync => Ok(()), 10 statements in total
  user: id integer not null, full_name character varying not null, email character varying not null, bio character varying
--- v11: comment.post_id becomes belongs_to post; user and post registered unchanged
  wire> ALTER TABLE "comment" ADD CONSTRAINT "fk-comment-post_id" FOREIGN KEY ("post_id") REFERENCES "post" ("id")
  sync => Ok(()), 13 statements in total
  user: id integer not null, full_name character varying not null, email character varying not null, bio character varying

--- e2: the enum gets a third variant
  wire> CREATE TYPE "t_status" AS ENUM ('draft', 'done', 'archived')
  wire< ErrorResponse 42710 type "t_status" already exists
  sync => Err("Execution Error: error returned from database: type \"t_status\" already exists at line 1167")
  tables in so_mig_sync: ["t", "t_extra"]

let r = if in_txn {
  let txn = db.begin().await?;
  match db.get_schema_registry("sync_txn::two::*").sync(&txn).await {
    Ok(()) => txn.commit().await,
    Err(e) => Err(e),
  }
} else {
  db.get_schema_registry("sync_txn::two::*").sync(&db).await
};

--- in_txn = false
  wire> ALTER TABLE "item" ADD COLUMN "note" varchar
  wire> ALTER TABLE "item" ADD COLUMN "code" varchar NOT NULL
  wire< ErrorResponse 23502 column "code" of relation "item" contains null values
  sync => Err("Execution Error: error returned from database: column \"code\" of relation \"item\" contains null values at line 6111")
  item columns: ["id", "note"]
--- in_txn = true
  wire> ALTER TABLE "item" ADD COLUMN "note" varchar
  wire> ALTER TABLE "item" ADD COLUMN "code" varchar NOT NULL
  wire< ErrorResponse 23502 column "code" of relation "item" contains null values
  sync => Err("Execution Error: error returned from database: column \"code\" of relation \"item\" contains null values at line 6111")
  item columns: ["id"]

--- v5: bio dropped from the entity, name: String -> Option<String>
  sync => Ok(()), 9 statements in total
  user: id integer not null, name character varying not null, email character varying not null, bio character varying