Added data migration steps

docs/data_migration.md

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+## 1. Create the target database
+
+First, create the target database `ihr-fastapi` where you want the tables and data to reside:
+
+
+## 2. Run Alembic migrations
+
+Run Alembic to create the schema and tables inside `ihr-fastapi`:
+
+```bash
+alembic upgrade head
+```
+
+This ensures the target database has all the required tables ready.
+
+---
+
+## 3. Connect to `ihr-fastapi` using psql
+
+Open a `psql` session to your target database:
+
+```bash
+psql -U <USERNAME> -d ihr-fastapi
+```
+
+Replace `<USERNAME>` with your PostgreSQL username.
+
+---
+## 4. Configure FDW to access the source database (`ihr`)
+
+Inside the `psql` session, run:
+
+```sql
+-- Enable the FDW extension
+CREATE EXTENSION IF NOT EXISTS postgres_fdw;
+
+-- Create a connection to the ihr DB
+CREATE SERVER "<SERVER_NAME>"
+FOREIGN DATA WRAPPER postgres_fdw
+OPTIONS (host '<HOST>', dbname '<DB_NAME>', port '<PORT>');
+
+-- Map your Postgres user to the remote DB credentials
+CREATE USER MAPPING FOR CURRENT_USER
+SERVER "<SERVER_NAME>"
+OPTIONS (user '<USERNAME>', password '<PASSWORD>');
+
+-- Import only the needed tables into a schema called ihr_src
+CREATE SCHEMA IF NOT EXISTS ihr_src;
+IMPORT FOREIGN SCHEMA public
+FROM SERVER "<SERVER_NAME>"
+INTO ihr_src;
+```
+
+Replace the following placeholders with your actual values:
+- `<SERVER_NAME>`: A name for your foreign server 
+- `<HOST>`: The hostname where your source database is running 
+- `<DB_NAME>`: The name of your source database 
+- `<PORT>`: The PostgreSQL port 
+- `<USERNAME>`: Your PostgreSQL username for the source database
+- `<PASSWORD>`: Your PostgreSQL password for the source database
+
+### Explanation
+
+* **`CREATE EXTENSION`** enables FDW support.
+* **`CREATE SERVER`** defines the connection to the source DB (`ihr`).
+* **`USER MAPPING`** maps your local PostgreSQL user to the remote DB user/password.
+* **`IMPORT FOREIGN SCHEMA`** pulls in table definitions into a local schema (`ihr_src`). These are **foreign tables** that point to the source DB.
+
+---
+
+## 5. Prepare to export migration SQL
+
+We’ll generate a file (`migration.sql`) with `INSERT ... SELECT` statements to copy the data.
+
+In `psql`, run:
+
+```sql
+\x off
+\pset format unaligned
+\pset pager off
+\pset tuples_only on
+\o migration.sql
+```
+
+### Explanation
+
+* **`\x off`** → disables expanded display.
+* **`\pset format unaligned`** → outputs raw SQL without table formatting.
+* **`\pset pager off`** → prevents paging.
+* **`\pset tuples_only on`** → suppresses headers/footers.
+* **`\o migration.sql`** → redirects all output into a file named `migration.sql`.
+
+---
+
+## 6. Generate the data migration SQL
+
+Run this query in `psql`:
+
+```sql
+SELECT 
+    'INSERT INTO public.' || table_name || ' (' ||
+    string_agg(column_name, ', ' ORDER BY ordinal_position) ||
+    ') SELECT ' ||
+    string_agg(column_name, ', ' ORDER BY ordinal_position) ||
+    ' FROM ihr_src.' || table_name ||
+    CASE 
+        WHEN EXISTS (
+            SELECT 1 FROM information_schema.columns c2
+            WHERE c2.table_schema = 'public' 
+            AND c2.table_name = c.table_name 
+            AND c2.column_name = 'timebin'
+        ) 
+        THEN ' WHERE timebin >= NOW() - INTERVAL ''3 months'';'
+        ELSE ';'
+    END ||
+    E'\n' ||
+    '\echo ''SUCCESS: ' || table_name || ' data inserted'''
+FROM information_schema.columns c
+WHERE table_schema = 'public' 
+AND table_name LIKE 'ihr_%'
+GROUP BY table_name
+ORDER BY table_name;
+```
+
+This builds a series of `INSERT INTO ... SELECT ...` statements that:
+
+* Copy all data from `ihr_src.table` to `public.table`.
+* If a `timebin` column exists, only copy rows from the **last 3 months**.
+* Print a confirmation message (`SUCCESS: ...`) after each table insert.
+
+---
+
+## 7. Exit `psql`
+
+Type:
+
+```sql
+\q
+```
+
+Now you’ll have a file called `migration.sql` in your current directory.
+
+---
+
+## 8. Run the migration
+
+Finally, execute the migration script against the `ihr-fastapi` database:
+
+```bash
+psql -U <USERNAME> -d ihr-fastapi -f migration.sql
+```
+
+This will insert data into all your new tables.

main.py

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     allow_origins=origins,
     allow_methods=["*"],
     allow_headers=["*"],
-)
+)