[QUESTION] Why entity.association('*') is not same as entity?.association?.('*') in cds-typer?

[ThePlenkov]

Question

HI! I have q very weird issue in my project.

Let's say i have a code like this:

const result = await SELECT.from(OBJECTS, (o) => {
    o.OBJECT_TYPE, o.OBJECT_OID, o.SCHEMA_NAME, o.OBJECT_NAME;
    o.view &&
      o.view((v) => {
        v('*');
        v.columns('*');
      });

By default it won't run because of the TS error:

Cannot invoke an object which is possibly 'undefined'.ts(2722)
(property) columns?: cds.ql.QLExtensions_<VIEW_COLUMNS_> | undefined

So here are two possible ways how to solve it:

• using condition

 o.view((v) => {
        v('*');
        v.columns && v.columns('*');
      });

and it works

• using optional notation ( also preferred by AI )

  o.view &&
      o.view((v) => {
        v('*');
        v?.columns?.('*');
      });

and this doesn't work!

Here is what I have in the console:

/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:876
        throw new Error(
              ^
Error: "call" not found in the elements of "VIEWS"
    at stepNotFoundInCombinedElements (/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:876:15)
    at /workspace/node_modules/@cap-js/db-service/lib/infer/index.js:576:13
    at Array.forEach (<anonymous>)
    at inferQueryElement (/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:529:18)
    at handleRef (/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:453:7)
    at /workspace/node_modules/@cap-js/db-service/lib/infer/index.js:331:16
    at Array.forEach (<anonymous>)
    at inferQueryElements (/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:300:15)
    at infer (/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:71:22)
    at resolveExpand (/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:842:42)

Do you know why? Thank you!

[ThePlenkov]

@chgeo do you know why? Can it be a bug? Thanks!

[daogrady]

Hi Petr,

thanks for filing this issue. I have transferred it to https://github.com/cap-js/cds-types as this is likely related to the types for the cds runtime, and probably has nothing to do with the generation of types for your model (cds-typer).

Can you share the type definition of OBJECTS?

Best,
Daniel

[ThePlenkov]

@daogrady THank you for looking into the issue. Types are generated - you can see them in a published package: https://www.npmjs.com/package/hana2cds?activeTab=code

Here is the source:
https://github.com/sapops/hana-cli/tree/main/packages/hana2cds/src/cds

Here is the place causing the error:
https://github.com/sapops/hana-cli/blob/main/packages/hana2cds/src/lib/hana2csn.ts#L22

[daogrady]

@sjvans / @johannes-vogel
user code looks fine on first glance. Nested projections should be allowed:

o.view((v /* type: { columns: Association to many { ... } } */) => {
  v('*');
  v?.columns?.('*');
});

the error seems to be thrown at runtime from the db-service module (see stacktrace in original post). Could you please have a look? Thanks!

[sjvans]

@patricebender should be able to assist

[patricebender]

Hi @ThePlenkov,

please provide steps to reproduce the error:

/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:876
        throw new Error(
              ^
Error: "call" not found in the elements of "VIEWS"
    at stepNotFoundInCombinedElements (/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:876:15)
    at /workspace/node_modules/@cap-js/db-service/lib/infer/index.js:576:13
    at Array.forEach (<anonymous>)
    at inferQueryElement (/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:529:18)
    at handleRef (/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:453:7)
    at /workspace/node_modules/@cap-js/db-service/lib/infer/index.js:331:16
    at Array.forEach (<anonymous>)
    at inferQueryElements (/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:300:15)
    at infer (/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:71:22)
    at resolveExpand (/workspace/node_modules/@cap-js/db-service/lib/infer/index.js:842:42)

Thank you
Patrice

[ThePlenkov]

@patricebender Hi Patrcie, of course. Here it is:

• clone https://github.com/ThePlenkov/sample-cap-cds-isssue
• npm install
• npm test

You will see that there will be two tests, one is working ( with conditional guards ) and one is not working with optional notation.

[patricebender]

@ThePlenkov thanks for providing the sample, I was able to reproduce the issue.

@sjvans i looks like an issue with the query builder API:

  const query = SELECT.from(OBJECTS, (o) => {
    o.OBJECT_TYPE, o.OBJECT_OID, o.SCHEMA_NAME, o.OBJECT_NAME;
    o?.view?.((t) => {
      t("*");
      t?.columns?.("*");
    });
  });
  console.log(JSON.stringify(query, null, 2));

yields:

{
      "SELECT": {
        "from": {
          "ref": [
            "OBJECTS"
          ]
        },
        "columns": [
          {
            "ref": [
              "OBJECT_TYPE"
            ]
          },
          {
            "ref": [
              "OBJECT_OID"
            ]
          },
          {
            "ref": [
              "SCHEMA_NAME"
            ]
          },
          {
            "ref": [
              "OBJECT_NAME"
            ]
          },
          { // from here on, the query looks very wrong 💥
            "ref": [
              "call" 
            ],
            "as": "undefined"
          },
          {
            "ref": [
              "raw"
            ]
          },
          {
            "ref": [
              "0"
            ]
          },
          {
            "ref": [
              null,
              "next",
              "done"
            ],
            "expand": [
              "*"
            ]
          }
        ]
      }
    }

→ cds.infer rightfully issues an error for the ref: [ "call" ] as there is no element call. Also the following refs look also as something went wrong.

[ThePlenkov]

@patricebender may be we can label then it as a bug, not question, thanks!

[ThePlenkov]

I also thought of something - why is it even optional? I mean if it's non-optional on the type level, then it's not even the error for TS. What could be the cases when some column references are undefined in the projection function?
Thanks!

[daogrady]

@patricebender can you please assign this issue to someone who is familiar with the query builder api? Thanks!

[sjvans]

i added it to the team backlog

[David-Kunz]

Hi,

The projection function only allows specific operations:

• projections are single-argument arrow functions: a => { ... }
• with the argument as entity alias in column expressions: a.name
• with functions for nested projections: a.books (b => {...})
• with * as special case of that: b.* , and b.suppliers('*')
• with template strings for aliases: b.createdAtas since
• as well as for infix filters: b.suppliers[city='Paris']

It allows you to statically define which columns of your entity you want to select. Technically, a JavaScript Proxy is used to execute some logic once a certain field is accessed, e.g. in

SELECT.from(MyEntity, e => { e.ID /* <-- field access */ })

There must not be any conditional operator and there shouldn't be a need for it. The corresponding TypeScript type should not complain that some properties might be undefined. It must be possible to follow every navigation of that entity, without checking for its existence. For example, it must be possible to write

const result = await SELECT.from(OBJECTS, (o) => {
    o.OBJECT_TYPE, o.OBJECT_OID, o.SCHEMA_NAME, o.OBJECT_NAME,
    o.view((v) => {
        v('*'),
        v.columns('*');
      });
})

@daogrady , do you think we can make sure that the above code works w.r.t. TypeScript?

[daogrady]

Hi David,

thanks for weighing in on this! I guess we should be able to express that properties, in the context of projections, are not optional. I will look into it.

Best,
Daniel