Create a Database Adapter

Learn how to create a custom database adapter for Better-Auth using createAdapter.

Our createAdapter function is designed to be very flexible, and we've done our best to make it easy to understand and use. Our hope is to allow you to focus on writing database logic, and not have to worry about how the adapter is working with Better-Auth.

Anything from custom schema configurations, custom ID generation, safe JSON parsing, and more is handled by the createAdapter function. All you need to do is provide the database logic, and the createAdapter function will handle the rest.

Quick Start

import { createAdapter, type AdapterDebugLogs } from "better-auth/adapters";
 
// Your custom adapter config options
interface CustomAdapterConfig {
  /**
   * Helps you debug issues with the adapter.
   */
  debugLogs?: AdapterDebugLogs;
  /**
   * If the table names in the schema are plural.
   */
  usePlural?: boolean;
}
 
export const myAdapter = (config: CustomAdapterConfig = {}) =>
  createAdapter({
    // ...
  });

// ...
export const myAdapter = (config: CustomAdapterConfig = {}) =>
  createAdapter({
    config: {
      adapterId: "custom-adapter", // A unique identifier for the adapter.
      adapterName: "Custom Adapter", // The name of the adapter.
      usePlural: config.usePlural ?? false, // Whether the table names in the schema are plural.
      debugLogs: config.debugLogs ?? false, // Whether to enable debug logs.
      supportsJSON: false, // Whether the database supports JSON. (Default: false)
      supportsDates: true, // Whether the database supports dates. (Default: true)
      supportsBooleans: true, // Whether the database supports booleans. (Default: true)
      supportsNumericIds: true, // Whether the database supports auto-incrementing numeric IDs. (Default: true)
    },
    // ...
  });

// ...
export const myAdapter = (config: CustomAdapterConfig = {}) =>
  createAdapter({
    config: {
      // ...
    },
    adapter: ({}) => {
      return {
        create: async ({ data, model, select }) => {
          // ...
        },
        update: async ({ data, model, select }) => {
          // ...
        },
        updateMany: async ({ data, model, select }) => {
          // ...
        },
        delete: async ({ data, model, select }) => {
          // ...
        },
        // ...
      };
    },
  });

Adapter

The adapter function is where you write the code that interacts with your database.

If you haven't already, check out the options object in the config section, as it can be useful for your adapter.

Before we get into the adapter function, let's go over the parameters that are available to you.

• options: The Better Auth options.
• schema: The schema from the user's Better Auth instance.
• debugLog: The debug log function.
• getField: The get field function.
• getDefaultModelName: The get default model name function.
• getDefaultFieldName: The get default field name function.
• getFieldAttributes: The get field attributes function.

adapter: ({
  options,
  schema,
  debugLog,
  getField,
  getDefaultModelName,
  getDefaultFieldName,
}) => {
  return {
    // ...
  };
};

Adapter Methods

• All model values are already transformed into the correct model name for the database based on the end-user's schema configuration.
  • This also means that if you need access to the schema version of a given model, you can't use this exact model value, you'll need to use the getDefaultModelName function provided in the options to convert the model to the schema version.
• We will automatically fill in any missing fields you return based on the user's schema configuration.
• Any method that includes a select parameter, is only for the purpose of getting data from your database more efficiently. You do not need to worry about only returning what the select parameter states, as we will handle that for you.

create method

The create method is used to create a new record in the database.

parameters:

• model: The model/table name that new data will be inserted into.
• data: The data to insert into the database.
• select: An array of fields to return from the database.

create: async ({ model, data, select }) => {
  // Example of inserting data into the database.
  return await db.insert(model).values(data);
};

update method

The update method is used to update a record in the database.

parameters:

• model: The model/table name that the record will be updated in.
• where: The where clause to update the record by.
• update: The data to update the record with.

update: async ({ model, where, update }) => {
  // Example of updating data in the database.
  return await db.update(model).set(update).where(where);
};

updateMany method

The updateMany method is used to update multiple records in the database.

parameters:

• model: The model/table name that the records will be updated in.
• where: The where clause to update the records by.
• update: The data to update the records with.

updateMany: async ({ model, where, update }) => {
  // Example of updating multiple records in the database.
  return await db.update(model).set(update).where(where);
};

delete method

The delete method is used to delete a record from the database.

parameters:

• model: The model/table name that the record will be deleted from.
• where: The where clause to delete the record by.

delete: async ({ model, where }) => {
  // Example of deleting a record from the database.
  await db.delete(model).where(where);
}

deleteMany method

The deleteMany method is used to delete multiple records from the database.

parameters:

• model: The model/table name that the records will be deleted from.
• where: The where clause to delete the records by.

deleteMany: async ({ model, where }) => {
  // Example of deleting multiple records from the database.
  return await db.delete(model).where(where);
};

findOne method

The findOne method is used to find a single record in the database.

parameters:

• model: The model/table name that the record will be found in.
• where: The where clause to find the record by.
• select: The select clause to return.

findOne: async ({ model, where, select }) => {
  // Example of finding a single record in the database.
  return await db.select().from(model).where(where).limit(1);
};

findMany method

The findMany method is used to find multiple records in the database.

parameters:

• model: The model/table name that the records will be found in.
• where: The where clause to find the records by.
• limit: The limit of records to return.
• sortBy: The sortBy clause to sort the records by.
• offset: The offset of records to return.

findMany: async ({ model, where, limit, sortBy, offset }) => {
  // Example of finding multiple records in the database.
  return await db
    .select()
    .from(model)
    .where(where)
    .limit(limit)
    .offset(offset)
    .orderBy(sortBy);
};

count method

The count method is used to count the number of records in the database.

parameters:

• model: The model/table name that the records will be counted in.
• where: The where clause to count the records by.

count: async ({ model, where }) => {
  // Example of counting the number of records in the database.
  return await db.select().from(model).where(where).count();
};

options (optional)

The options object is for any potential config that you got from your custom adapter options.

const myAdapter = (config: CustomAdapterConfig) =>
  createAdapter({
    config: {
      // ...
    },
    adapter: ({ options }) => {
      return {
        options: config,
      };
    },
  });

createSchema (optional)

The createSchema method allows the Better Auth CLI to generate a schema for the database.

parameters:

• tables: The tables from the user's Better-Auth instance schema; which is expected to be generated into the schema file.
• file: The file the user may have passed in to the generate command as the expected schema file output path.

createSchema: async ({ file, tables }) => {
  // ... Custom logic to create a schema for the database.
};

Test your adapter

We've provided a test suite that you can use to test your adapter. It requires you to use vitest.

import { expect, test, describe } from "vitest";
import { runAdapterTest } from "better-auth/adapters/test";
import { myAdapter } from "./my-adapter";
 
describe("My Adapter Tests", async () => {
  afterAll(async () => {
    // Run DB cleanup here...
  });
  const adapter = myAdapter({
    debugLogs: {
      // If your adapter config allows passing in debug logs, then pass this here.
      isRunningAdapterTests: true, // This is our super secret flag to let us know to only log debug logs if a test fails.
    },
  });
 
  await runAdapterTest({
    getAdapter: async (betterAuthOptions = {}) => {
      return adapter(betterAuthOptions);
    },
  });
});

Numeric ID tests

If your database supports numeric IDs, then you should run this test as well:

import { expect, test, describe } from "vitest";
import { runNumberIdAdapterTest } from "better-auth/adapters/test";
import { myAdapter } from "./my-adapter";
 
describe("My Adapter Numeric ID Tests", async () => {
  afterAll(async () => {
    // Run DB cleanup here...
  });
  const adapter = myAdapter({
    debugLogs: {
      // If your adapter config allows passing in debug logs, then pass this here.
      isRunningAdapterTests: true, // This is our super secret flag to let us know to only log debug logs if a test fails.
    },
  });
 
  await runNumberIdAdapterTest({
    getAdapter: async (betterAuthOptions = {}) => {
      return adapter(betterAuthOptions);
    },
  });
});

Config

The config object is used to provide information about the adapter to Better-Auth.

We highly recommend going through and reading each provided option below, as it will help you understand how to properly configure your adapter.

Required Config

adapterId

A unique identifier for the adapter.

adapterName

The name of the adapter.

Optional Config

supportsNumericIds

Whether the database supports numeric IDs. If this is set to false and the user's config has enabled useNumberId, then we will throw an error.

supportsJSON

Whether the database supports JSON. If the database doesn't support JSON, we will use a string to save the JSON data.And when we retrieve the data, we will safely parse the string back into a JSON object.

supportsDates

Whether the database supports dates. If the database doesn't support dates, we will use a string to save the date. (ISO string) When we retrieve the data, we will safely parse the string back into a Date object.

supportsBooleans

Whether the database supports booleans. If the database doesn't support booleans, we will use a 0 or 1 to save the boolean value. When we retrieve the data, we will safely parse the 0 or 1 back into a boolean value.

usePlural

Whether the table names in the schema are plural. This is often defined by the user, and passed down through your custom adapter options. If you do not intend to allow the user to customize the table names, you can ignore this option, or set this to false.

const adapter = myAdapter({
  // This value then gets passed into the `usePlural`
  // option in the createAdapter `config` object.
  usePlural: true,
});

debugLogs

Used to enable debug logs for the adapter. You can pass in a boolean, or an object with the following keys: create, update, updateMany, findOne, findMany, delete, deleteMany, count. If any of the keys are true, the debug logs will be enabled for that method.

// Will log debug logs for all methods.
const adapter = myAdapter({
  debugLogs: true,
});

// Will only log debug logs for the `create` and `update` methods.
const adapter = myAdapter({
  debugLogs: {
    create: true,
    update: true,
  },
});

disableIdGeneration

Whether to disable ID generation. If this is set to true, then the user's generateId option will be ignored.

customIdGenerator

If your database only supports a specific custom ID generation, then you can use this option to generate your own IDs.

mapKeysTransformInput

If your database uses a different key name for a given situation, you can use this option to map the keys. This is useful for databases that expect a different key name for a given situation. For example, MongoDB uses _id while in Better-Auth we use id.

Each key in the returned object represents the old key to replace. The value represents the new key.

This can be a partial object that only transforms some keys.

mapKeysTransformInput: () => {
  return {
    id: "_id", // We want to replace `id` to `_id` to save into MongoDB
  };
},

mapKeysTransformOutput

If your database uses a different key name for a given situation, you can use this option to map the keys. This is useful for databases that use a different key name for a given situation. For example, MongoDB uses _id while in Better-Auth we use id.

Each key in the returned object represents the old key to replace. The value represents the new key.

This can be a partial object that only transforms some keys.

mapKeysTransformOutput: () => {
  return {
    _id: "id", // We want to replace `_id` (from MongoDB) to `id` (for Better-Auth)
  };
},

customTransformInput

If you need to transform the input data before it is saved to the database, you can use this option to transform the data.

The customTransformInput function receives the following arguments:

• data: The data to transform.
• field: The field that is being transformed.
• fieldAttributes: The field attributes of the field that is being transformed.
• select: The select values which the query expects to return.
• model: The model that is being transformed.
• schema: The schema that is being transformed.
• options: Better Auth options.

The customTransformInput function runs at every key in the data object of a given action.

customTransformInput: ({ field, data }) => {
  if (field === "id") {
    return "123"; // Force the ID to be "123"
  }
 
  return data;
};

customTransformOutput

If you need to transform the output data before it is returned to the user, you can use this option to transform the data. The customTransformOutput function is used to transform the output data. Similar to the customTransformInput function, it runs at every key in the data object of a given action, but it runs after the data is retrieved from the database.

customTransformOutput: ({ field, data }) => {
  if (field === "name") {
    return "Bob"; // Force the name to be "Bob"
  }
 
  return data;
};

const some_data = await adapter.create({
  model: "user",
  data: {
    name: "John",
  },
});
 
// The name will be "Bob"
console.log(some_data.name);