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Transactions

Eden-MDBS supports atomic transactions for executing multiple database operations as a single unit of work. This guide covers single-endpoint transactions and considerations for cross-database operations.

What Are Transactions?

Transactions ensure that a group of operations either all succeed or all fail together, maintaining data consistency. This is essential for operations like:

  • Transferring funds between accounts
  • Creating related records across multiple tables
  • Updating inventory and order status together

Single-Endpoint Transactions

Basic Transaction

Execute multiple operations atomically on a single endpoint:

bash
curl http://{host}:8000/api/v1/endpoints/my_postgres/transaction \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $TOKEN" \
  -d '{
    "operations": [
      {
        "query": "UPDATE accounts SET balance = balance - $1 WHERE id = $2",
        "params": [100.00, 1]
      },
      {
        "query": "UPDATE accounts SET balance = balance + $1 WHERE id = $2",
        "params": [100.00, 2]
      },
      {
        "query": "INSERT INTO transactions (from_id, to_id, amount, created_at) VALUES ($1, $2, $3, NOW())",
        "params": [1, 2, 100.00]
      }
    ]
  }'

Response:

json
{
  "status": "success",
  "data": {
    "results": [
      {"rows_affected": 1},
      {"rows_affected": 1},
      {"rows_affected": 1}
    ]
  }
}

Transaction Behavior

  • Atomicity: All operations succeed or all are rolled back
  • Isolation: Intermediate states are not visible to other transactions
  • Order: Operations execute in the order provided

Transaction with RETURNING

Capture results from individual operations:

bash
curl http://{host}:8000/api/v1/endpoints/my_postgres/transaction \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $TOKEN" \
  -d '{
    "operations": [
      {
        "query": "INSERT INTO orders (user_id, total) VALUES ($1, $2) RETURNING id",
        "params": [123, 299.99]
      },
      {
        "query": "INSERT INTO order_items (order_id, product_id, quantity) VALUES ($1, $2, $3)",
        "params": ["{{result[0].id}}", 456, 2]
      }
    ]
  }'

Common Transaction Patterns

Financial Transfer

bash
curl http://{host}:8000/api/v1/endpoints/my_postgres/transaction \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $TOKEN" \
  -d '{
    "operations": [
      {
        "query": "UPDATE accounts SET balance = balance - $1 WHERE id = $2 AND balance >= $1",
        "params": [500.00, 1]
      },
      {
        "query": "UPDATE accounts SET balance = balance + $1 WHERE id = $2",
        "params": [500.00, 2]
      },
      {
        "query": "INSERT INTO audit_log (action, amount, from_account, to_account) VALUES ($1, $2, $3, $4)",
        "params": ["transfer", 500.00, 1, 2]
      }
    ]
  }'

Inventory and Order

bash
curl http://{host}:8000/api/v1/endpoints/my_postgres/transaction \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $TOKEN" \
  -d '{
    "operations": [
      {
        "query": "UPDATE inventory SET quantity = quantity - $1 WHERE product_id = $2 AND quantity >= $1",
        "params": [5, 789]
      },
      {
        "query": "INSERT INTO orders (customer_id, product_id, quantity, status) VALUES ($1, $2, $3, $4)",
        "params": [123, 789, 5, "pending"]
      }
    ]
  }'

Cascading Updates

bash
curl http://{host}:8000/api/v1/endpoints/my_postgres/transaction \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $TOKEN" \
  -d '{
    "operations": [
      {
        "query": "UPDATE users SET status = $1, updated_at = NOW() WHERE id = $2",
        "params": ["inactive", 123]
      },
      {
        "query": "UPDATE sessions SET terminated_at = NOW() WHERE user_id = $1 AND terminated_at IS NULL",
        "params": [123]
      },
      {
        "query": "INSERT INTO user_status_history (user_id, old_status, new_status) VALUES ($1, $2, $3)",
        "params": [123, "active", "inactive"]
      }
    ]
  }'

Transaction Templates

Create reusable transaction templates:

bash
curl http://{host}:8000/api/v1/templates \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $TOKEN" \
  -d '{
    "id": "transfer_funds",
    "description": "Transfer funds between accounts",
    "template": {
      "endpoint_uuid": "550e8400-e29b-41d4-a716-446655440000",
      "kind": "Transaction",
      "template": {
        "operations": [
          {
            "query": "UPDATE accounts SET balance = balance - {{amount}} WHERE id = {{from_account}}",
            "params": ["{{amount}}", "{{from_account}}"]
          },
          {
            "query": "UPDATE accounts SET balance = balance + {{amount}} WHERE id = {{to_account}}",
            "params": ["{{amount}}", "{{to_account}}"]
          }
        ]
      },
      "endpoint_kind": "Postgres"
    }
  }'

Execute the template:

bash
curl http://{host}:8000/api/v1/templates/transfer_funds \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $TOKEN" \
  -X POST \
  -d '{
    "from_account": 1,
    "to_account": 2,
    "amount": 100.00
  }'

Error Handling

Transaction Rollback

If any operation fails, all previous operations are rolled back:

json
{
  "error": "Transaction failed",
  "message": "Operation 2 failed: insufficient funds",
  "details": {
    "failed_operation": 2,
    "rolled_back": true
  }
}

Common Errors

Constraint Violation:

json
{
  "error": "Transaction failed",
  "message": "violates check constraint \"accounts_balance_check\""
}

Deadlock:

json
{
  "error": "Transaction failed",
  "message": "deadlock detected"
}

Timeout:

json
{
  "error": "Transaction failed",
  "message": "lock wait timeout exceeded"
}

Access Control

Transactions require Write access to the endpoint:

Access LevelCan Execute Transactions
ReadNo
WriteYes
AdminYes
SuperAdminYes

Best Practices

Transaction Design

  • Keep transactions short: Long transactions hold locks longer
  • Order operations consistently: Helps prevent deadlocks
  • Include validation: Add checks (like balance >= amount) in your queries
  • Handle failures: Design your application to handle rollbacks gracefully

Performance

  • Minimize operations: Only include necessary operations
  • Use indexes: Ensure queries are optimized
  • Avoid nested transactions: Use a single flat transaction

Data Integrity

  • Use constraints: Let the database enforce rules
  • Include audit trails: Log important operations
  • Test edge cases: Verify behavior with concurrent access

Limitations

  • Transactions are scoped to a single endpoint
  • For cross-database operations, consider using workflows with compensating transactions
  • Maximum number of operations per transaction may be limited

Related

Last updated: October 20, 2018
Size: 7.24 KB
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