graphql recognizes decimal type now and successfully starts

backend/src/graphql/scalar/Decimal.ts

@@ -0,0 +1,26 @@
+import { GraphQLScalarType, Kind } from 'graphql'
+import Decimal from 'decimal.js-light'
+
+export default new GraphQLScalarType({
+  name: 'Decimal',
+  description: 'The `Decimal` scalar type to represent currency values',
+
+  serialize(value: unknown) {
+    if (!(value instanceof Decimal)) {
+      throw new Error('DecimalScalar can only serialize Decimal values')
+    }
+    return value.toString()
+  },
+
+  parseValue(value) {
+    return new Decimal(value)
+  },
+
+  parseLiteral(ast) {
+    if (ast.kind !== Kind.STRING) {
+      throw new TypeError(`${String(ast)} is not a valid decimal value.`)
+    }
+
+    return new Decimal(ast.value)
+  },
+})

backend/src/graphql/schema.ts

@@ -1,13 +1,16 @@
 import { GraphQLSchema } from 'graphql'
 import { buildSchema } from 'type-graphql'
+import Decimal from 'decimal.js-light'
 import path from 'path'
 
 import isAuthorized from './directive/isAuthorized'
+import DecimalScalar from './scalar/Decimal'
 
 const schema = async (): Promise<GraphQLSchema> => {
   return buildSchema({
     resolvers: [path.join(__dirname, 'resolver', `!(*.test).{js,ts}`)],
     authChecker: isAuthorized,
+    scalarsMap: [{ type: Decimal, scalar: DecimalScalar }],
   })
 }