Decimal methods not supported

Bug description

According to the docs, Decimal comes from the library Decimal.js. However, the methods from Decimal.js produce an error.

export const FormatPrice = (input: Decimal | null) => {
    const valueString = input === null ? "--" : input.toFixed(2);
    return valueString;
};

This produces an unhandled runtime error: input.toFixed is not a function.

Is prisma’s Decimal a complete implementation of Decimal.js or some sort of subset?

How to reproduce

In a project that has a Decimal data type, create a function to format Decimal values:

export const FormatPrice = (input: Decimal | null) => {
    const valueString = input === null ? "--" : input.toFixed(2);
    return valueString;
};

The function will not compile.

Expected behavior

No response

Prisma information

Environment & setup

• OS: Ubuntu, Windows
• Database: MySQL
• Node.js version: 16.13.0

Prisma Version

prisma                  : 4.0.0
@prisma/client          : 4.0.0
Current platform        : windows
Query Engine (Node-API) : libquery-engine da41d2bb3406da22087b849f0e911199ba4fbf11 (at node_modules\.pnpm\@[e-mail]41d2bb3406da22087b849f0e911199ba4fbf11\node_modules\@prisma\engines\query_engine-windows.dll.node)
Migration Engine        : migration-engine-cli da41d2bb3406da22087b849f0e911199ba4fbf11 (at node_modules\.pnpm\@[e-mail]41d2bb3406da22087b849f0e911199ba4fbf11\node_modules\@prisma\engines\migration-engine-windows.exe)
Introspection Engine    : introspection-core da41d2bb3406da22087b849f0e911199ba4fbf11 (at node_modules\.pnpm\@[e-mail]41d2bb3406da22087b849f0e911199ba4fbf11\node_modules\@prisma\engines\introspection-engine-windows.exe)
Format Binary           : prisma-fmt da41d2bb3406da22087b849f0e911199ba4fbf11 (at node_modules\.pnpm\@[e-mail]41d2bb3406da22087b849f0e911199ba4fbf11\node_modules\@prisma\engines\prisma-fmt-windows.exe)
Default Engines Hash    : da41d2bb3406da22087b849f0e911199ba4fbf11
Studio                  : 0.465.0
Preview Features        : referentialIntegrity

[SevInf]

@ChristianIvicevic @grahampcharles I don’t think this problem has anything to do with prisma. JSON.parse(JSON.stringify()) loop is where decimal instance gets lost. Decimal is not a thing in JSON, when you do stringify it is converted to string. JSON.parse then does not know anything about Decimal as well and parses value as regular string. You’ll have to manually convert decimal values to decimal instances after JSON.parse, there is no way around it.

Since it does not seem to be Prisma issue, I’ll close it for now. Feel free to reopen if you manage to reproduce it without JSON.parse(JSON.stringify()) part.

[grahampcharles]

Hm. Well first, there’s this: Today I learned that in Next.js, prisma objects must cross the getSSP -> component divide. (A similar thing would happen in vanilla React, I think?) It’s not readily clear that that step is going to involve serialization. So first off, I’d say that needs to be documented.

Second, it would seem that nearly everyone who uses prisma with React is going to run into a JSON serialization problem unless they’re only using primitive data types – and since prisma makes use of Decimal instead of number, that includes anyone using any kind of floating-point number. What does everyone else do in this situation? I ran into the problem on a date field and found that The Internet said to just put a parse(stringify()) around the object, but clearly that’s a bad idea.

Anyway, this is clearly a quirk of interaction between prisma (among other packages!) and React. Given that, yes, I think a helper function to fix the problem (an adapted superjson?) would be lovely. At least, some documentation of the issue would be a really good start.