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- // @flow strict
- import { GraphQLError } from '../../error/GraphQLError';
- import { type ASTVisitor } from '../../language/visitor';
- import { type OperationDefinitionNode } from '../../language/ast';
- import { type ASTValidationContext } from '../ValidationContext';
- export function singleFieldOnlyMessage(name: ?string): string {
- return name
- ? `Subscription "${name}" must select only one top level field.`
- : 'Anonymous Subscription must select only one top level field.';
- }
- export function SingleFieldSubscriptions(
- context: ASTValidationContext,
- ): ASTVisitor {
- return {
- OperationDefinition(node: OperationDefinitionNode) {
- if (node.operation === 'subscription') {
- if (node.selectionSet.selections.length !== 1) {
- context.reportError(
- new GraphQLError(
- singleFieldOnlyMessage(node.name && node.name.value),
- node.selectionSet.selections.slice(1),
- ),
- );
- }
- }
- },
- };
- }
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