KeystoneJS Custom Fields Development

Custom Fields Development in KeystoneJS

Built-in KeystoneJS fields (text, integer, relationship, image) cover most cases, but sometimes specialized storage logic or unique Admin UI is needed. Custom fields are full-fledged extensions with database types, GraphQL resolvers, and React components for Admin UI.

Custom Field Architecture

Custom field in KeystoneJS consists of three layers:

1. DB Layer — how data is stored in Prisma/DB (one or more columns)
2. GraphQL Layer — types for read/write via API
3. Admin UI Layer — React components for display and editing

fieldType(dbConfig)
  ├── getAdminMeta()        // UI metadata
  ├── views (React)
  │   ├── Field             // edit component
  │   ├── Cell              // list cell
  │   ├── CardValue         // relationship card display
  │   └── controller.ts     // client logic
  └── graphql
      ├── input             // mutation type
      ├── output            // query type
      └── filters           // where-filter types

Example: Phone Number Field with Formatting

Field stores phone as string but provides UI with input mask and format validation.

// fields/phoneNumber/index.ts
import {
  fieldType,
  FieldTypeFunc,
  BaseListTypeInfo,
  FieldData,
} from '@keystone-6/core/types';
import { graphql } from '@keystone-6/core';

type PhoneNumberConfig<ListTypeInfo extends BaseListTypeInfo> = {
  validation?: { isRequired?: boolean };
  defaultValue?: string;
  isIndexed?: boolean | 'unique';
  db?: { isNullable?: boolean; map?: string };
};

export function phoneNumber<ListTypeInfo extends BaseListTypeInfo>(
  config: PhoneNumberConfig<ListTypeInfo> = {}
): FieldTypeFunc<ListTypeInfo> {
  return (meta: FieldData) => {
    const {
      validation: { isRequired = false } = {},
      isIndexed = false,
      defaultValue,
    } = config;

    return fieldType({
      kind: 'scalar',
      mode: isRequired ? 'required' : 'optional',
      scalar: 'String',
      isIndexed,
      default: defaultValue ? { kind: 'literal', value: defaultValue } : undefined,
    })({
      ...meta,
      hooks: {
        validateInput: async ({ resolvedData, fieldKey, addValidationError }) => {
          const value = resolvedData[fieldKey];
          if (value === undefined || value === null) return;

          // Validation: digits, +, -, spaces, brackets
          const phoneRegex = /^\+?[\d\s\-()]{7,20}$/;
          if (!phoneRegex.test(value)) {
            addValidationError(`Invalid phone format: ${value}`);
          }
        },
      },
      input: {
        create: {
          arg: graphql.arg({ type: graphql.String }),
          resolve: (value) => (value ? normalizePhone(value) : null),
        },
        update: {
          arg: graphql.arg({ type: graphql.String }),
          resolve: (value) => (value === undefined ? undefined : value ? normalizePhone(value) : null),
        },
      },
      output: graphql.field({ type: graphql.String }),
      views: require.resolve('./views'),
      getAdminMeta: () => ({ isRequired }),
    });
  };
}

function normalizePhone(phone: string): string {
  return phone.replace(/\s+/g, '').replace(/[()]/g, '');
}

// fields/phoneNumber/views.tsx
import React, { useState } from 'react';
import { FieldProps, controller } from '@keystone-6/core/fields';

export const Field = ({ field, value, onChange, autoFocus }: FieldProps<typeof controller>) => {
  const [inputValue, setInputValue] = useState(value || '');

  const handleChange = (e: React.ChangeEvent<HTMLInputElement>) => {
    const raw = e.target.value;
    setInputValue(raw);
    onChange?.(raw);
  };

  return (
    <div className="flex flex-col gap-1">
      <label className="font-medium text-sm">{field.label}</label>
      <input
        type="tel"
        value={inputValue}
        onChange={handleChange}
        autoFocus={autoFocus}
        placeholder="+1 (555) 123-4567"
        className="border rounded px-3 py-2 text-sm"
      />
      {field.adminMeta.isRequired && !value && (
        <span className="text-red-500 text-xs">Required field</span>
      )}
    </div>
  );
};

export const Cell = ({ item, field }) => (
  <span>{item[field.path] || '—'}</span>
);

export const CardValue = ({ item, field }) => (
  <span>{item[field.path] || 'Not set'}</span>
);

export const controller = (config) => ({
  path: config.path,
  label: config.label,
  description: config.description,
  adminMeta: config.fieldMeta,
  graphqlSelection: config.path,
  defaultValue: '',
  deserialize: (data) => data[config.path] ?? '',
  serialize: (value) => ({ [config.path]: value || null }),
  validate: (value) => {
    if (config.fieldMeta.isRequired && !value) return false;
    return true;
  },
});

Usage in List:

import { phoneNumber } from './fields/phoneNumber';

export const Customer = list({
  fields: {
    name: text({ validation: { isRequired: true } }),
    phone: phoneNumber({ validation: { isRequired: true }, isIndexed: true }),
    altPhone: phoneNumber(),
  },
});

Timeline

Publishing as npm package for reuse across projects adds 0.5–1 day for build setup and documentation.