graphql/validation/rules/LoneSchemaDefinitionRule.mjs

A Query Language and Runtime which can target any service.

import { GraphQLError } from "../../error/GraphQLError.mjs";
export function LoneSchemaDefinitionRule(context) {
    const oldSchema = context.getSchema();
    const alreadyDefined = oldSchema?.astNode ??
        oldSchema?.getQueryType() ??
        oldSchema?.getMutationType() ??
        oldSchema?.getSubscriptionType();
    let schemaDefinitionsCount = 0;
    return {
        SchemaDefinition(node) {
            if (alreadyDefined) {
                context.reportError(new GraphQLError('Cannot define a new schema within a schema extension.', { nodes: node }));
                return;
            }
            if (schemaDefinitionsCount > 0) {
                context.reportError(new GraphQLError('Must provide only one schema definition.', {
                    nodes: node,
                }));
            }
            ++schemaDefinitionsCount;
        },
    };
}
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