make primary column optional

error message:

Use @PrimaryColumn decorator to add a primary column to your entity.

import { Column, Entity, Index } from "typeorm";

@Index("biARBL", ["co", "mth", "batchId", "batchSeq", "arLine"], {
  unique: true,
})
@Index(
  "biARBLApplied",
  ["co", "applyMth", "applyTrans", "applyLine", "mth", "batchId", "batchSeq"],
  {},
)
@Entity("bARBL", { schema: "dbo" })
export class BArbl {
  @Column("tinyint", { name: "Co" })
  co: number;

  @Column("smalldatetime", { name: "Mth" })
  mth: Date;

  @Column("int", { name: "BatchId" })
  batchId: number;

  @Column("int", { name: "BatchSeq" })
  batchSeq: number;

  @Column("smallint", { name: "ARLine", nullable: true })
  arLine: number | null;

  @Column("char", { name: "TransType", length: 1 })
  transType: string;
}

I can’t add @PimaryColumn on all fields of my index because one of them arLine is nullable.

_Originally posted by @saostad in https://github.com/typeorm/typeorm/issues/3704#issuecomment-573211839_

[Kononnable]

Typeorm requires entity to have primary key defined to work correctly and there are no plans to change that. If you don’t want to use primary key(or you’re forced not to use it) you can mark unique index as primary key and disable schema sync for such table. It would deceive ORM and you should be able to use such table.

[Maddimax]

you can mark unique index as primary key

How can I mark a unique index as a primary key? I could not find anything in the documentation.