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## Query Across SQL and NoSQL — Without Writing Code |
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MongoDB and PostgreSQL are often used together in modern applications — each bringing unique strengths. While PostgreSQL offers structured, relational storage, MongoDB gives flexibility through document-based collections. |
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But combining data from both in real time has always been a challenge. Traditionally, you’d have to: |
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- Write custom backend logic to merge data |
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- Create multiple API calls or aggregation pipelines |
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- Maintain sync through fragile ETL workflows |
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To solve this challenge, API Maker introduces the **Find & Join** feature. |
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## Why Use Find & Join for MongoDB and PostgreSQL |
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Modern applications often use a **polyglot database architecture** — leveraging **MongoDB** for unstructured or flexible data and **PostgreSQL** for structured, relational data. |
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While this separation is practical from a design and performance standpoint, it introduces a major challenge: |
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**How do you fetch connected data across MongoDB and PostgreSQL in a single query** — without building and maintaining complex backend logic? |
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This is exactly where **API Maker’s Find & Join feature** shines. |
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It allows you to **perform deep, cross-database joins and filters between MongoDB and PostgreSQL** using a single, declarative JSON query — all through REST APIs. |
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This page provides information on using the Find & Join feature specifically with MongoDB and PostgreSQL. |
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If you're looking for a general overview of the Find & Join feature, please refer to the - [Find & Join Feature](https://apimaker.dev/find-and-join) |
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## Schema Setup in Api Maker |
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To enable Find & Join operations between MongoDB and PostgreSQL, you need to define relationships in your table/collection schema using **API Maker’s Table schema.** |
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For a Detailed Information about the Schema Setup, you can refer to this page - [Schema Setup](https://docs.apimaker.dev/v1/docs/schema/schema.html) |
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Once the schema is defined, API Maker can automatically resolve joins at runtime — even across different database types. |
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### Defining the Relationship in Schema |
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Let’s say: |
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- You have a **`users`** table in **PostgreSQL** |
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- You have a **`profiles`** collection in **MongoDB** |
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You want to use an API that supports the **Find & Join** feature on the `profiles` collection (MongoDB). In this case, you'd define the relationship like this: |
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```typescript |
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user_id: <ISchemaProperty>{ |
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__type: EType.number, |
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instance: "Postgres", |
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database: "accounts_db", |
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table: "users", |
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column: "id" |
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} |
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``` |
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Here what each field means: |
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- **`__type: EType.number :`** Indicates that the `user_id` field is a number (to match the PostgreSQL `id` column type). |
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- **`instance: "Postgres" :`** Specifies the target database engine — in this case, PostgreSQL. |
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- **`database: "accounts_db" :`** The name of the PostgreSQL database where the `users` table resides. |
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- **`table: "users" :`** The relational table in PostgreSQL to which the `user_id` field will be linked. |
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- **`column: "id" :`** The specific column in the `users` table that the `user_id` field refers to. |
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With this schema defined, API Maker can: |
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- Automatically recognize and resolve the relationship between MongoDB and PostgreSQL |
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- Enable join queries like `user_id.name` directly in your REST API calls |
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- Eliminate the need for custom backend join logic — it's all handled for you at runtime |
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## Sample Query Examples : |
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Once you've defined relationships between your MongoDB collections and PostgreSQL tables in the schema, you can use the **Find & Join** feature directly in your API calls — without writing any backend logic. |
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API Maker supports the Find & Join Feature in both the : |
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- **GET requests** (using URL query parameters) |
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- **POST requests** (using request body for advanced querying) |
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### **Example Scenario** |
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You have: |
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- A `users` table in **PostgreSQL** |
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- A `profiles` collection in **MongoDB** with a field `user_id` referencing `users.id` |
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**1. GET API Example (Using URL Query Parameter) :** |
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Use the `find` Query parameter in your auto-generated GET API to filter across relationships. |
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**Request:** |
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```http |
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GET /api/profiles?find={ "user_id.name": "Alice" } |
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``` |
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This query fetches all `profiles` (from MongoDB) where the related `user` (from PostgreSQL) has the name `"Alice"`. |
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**2. POST API Example :** |
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POST APIs give you more flexibility — allowing you to send a `find` object along with additional options like `sort`, `limit`, and `deep`. |
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**Request:** |
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```http |
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POST /api/query/profiles |
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Content-Type: application/json |
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{ |
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"find": { |
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"user_id.signup_date": { "$gt": "2024-01-01" }, |
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"user_id.role": "admin" |
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}, |
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"limit": 10, |
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"sort": { |
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"user_id.signup_date": -1 |
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} |
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} |
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``` |
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This will return up to 10 profiles linked to PostgreSQL users who signed up after January 1st, 2024 and have the role `"admin"` — sorted by most recent signup. |
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To explore all REST APIs that support **Find & Join**, check out the [auto-generated REST APIs](https://docs.apimaker.dev/v1/docs/apis-all/generated-apis/auto-generated-get-all-api.html) and [schema-based REST APIs](https://docs.apimaker.dev/v1/docs/apis-all/schema-apis/auto-generated-schema-based-get-all-api.html) available on the [API Maker Docs Page](https://docs.apimaker.dev/). |
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## Comparison to Traditional Methods & Other Platforms |
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Joining data between **MongoDB** and **PostgreSQL** has traditionally been a complex, manual process for developers. |
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**Traditional Methods:** |
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Before tools like API Maker, developers had to: |
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- Write custom backend code to connect and query both databases |
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- Manually merge results at the application level |
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- Build and maintain fragile ETL pipelines |
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- Handle sync issues and performance bottlenecks |
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These methods are time-consuming and hard to scale — especially when relationships become more complex. |
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How API Maker Simplifies Cross Database Joins and Conditional Filtering : |
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- **No backend logic** required |
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- **Schema-based joins** resolved automatically at runtime |
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- **Real-time querying** across different databases |
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- Simple REST API interface — easy to use from frontend or backend |
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### Compared to Other Platforms |
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| Feature | **API Maker** | **Appwrite** | **Supabase** | **Firebase** | |
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| ----------------------------- | ------------- | ------------ | ------------ | -------------- | |
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| Cross-DB Joins (Mongo + SQL) | Yes | No | No | No | |
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| N-Level Nested Joins | Unlimited | No | Basic | No | |
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| REST Support for Join Queries | Full | Partial | Yes | Firestore only | |
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| Schema-Based Join Logic | Yes | No | Limited | No | |
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| Works with Mongo + PostgreSQL | Yes | No | No | No | |
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**API Maker** is the only platform among these that offers **real-time, schema-aware, cross database joins** between MongoDB and PostgreSQL — with **no backend logic required**. |
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## FAQ's |
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1. **Can I join MongoDB collections with PostgreSQL tables in both directions?** |
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Yes. As long as the relationship is defined in your schema, you can perform joins in either direction — **`MongoDB`** → **`PostgreSQL`** or **`PostgreSQL`** → **`MongoDB`** — using the same query structure. |
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2. **How do I filter on PostgreSQL fields from within a MongoDB collection?** |
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You can use nested dot notation based on your schema definition. |
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For example: `{ "user_id.role": "admin" }`. |
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In this case, `user_id` is a reference from the MongoDB `profiles` collection to the PostgreSQL `users` table. |
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3. **Is performance impacted by cross-database joins?** |
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API Maker optimizes cross-database joins at runtime. |
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For best performance, make sure to **index the join keys** in both MongoDB and PostgreSQL. |
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