Frequently Asked Questions¶

Getting Started¶

How do I create a new object?¶

// Method 1: Using typed constructor
var Customer := TCustomer.Create(BoldSystem);

// Method 2: Using class extent
var Customer := BoldSystem.Classes['Customer'].CreateNewObject as TCustomer;

How do I save changes to the database?¶

BoldSystemHandle1.UpdateDatabase;
// or
BoldSystem.UpdateDatabase;

How do I delete an object?¶

Customer.Delete;
BoldSystem.UpdateDatabase;  // Actually removes from DB

How do I check for unsaved changes?¶

if BoldSystem.DirtyObjects.Count > 0 then
  ShowMessage('You have unsaved changes');

OCL Queries¶

How do I get all instances of a class?¶

// Method 1: OCL
var Customers := BoldSystem.EvaluateExpressionAsNewElement(
  'Customer.allInstances', nil) as TBoldObjectList;

// Method 2: Direct access
var Customers := BoldSystem.Classes['Customer'].BoldObjects;

How do I filter objects?¶

// Find active customers
var ActiveCustomers := BoldSystem.EvaluateExpressionAsNewElement(
  'Customer.allInstances->select(active = true)', nil) as TBoldObjectList;

// Find customers with orders
var CustomersWithOrders := BoldSystem.EvaluateExpressionAsNewElement(
  'Customer.allInstances->select(orders->notEmpty)', nil) as TBoldObjectList;

How do I sort a list?¶

// Sort by name
var Sorted := BoldSystem.EvaluateExpressionAsNewElement(
  'Customer.allInstances->orderBy(name)', nil) as TBoldObjectList;

// Sort descending
var Sorted := BoldSystem.EvaluateExpressionAsNewElement(
  'Customer.allInstances->orderDescending(createdDate)', nil) as TBoldObjectList;

How do I calculate a sum?¶

var Total := BoldSystem.EvaluateExpressionAsFloat(
  'Order.allInstances->collect(total)->sum', nil);

Associations¶

How do I link two objects?¶

// One-to-many: Add order to customer
Customer.Orders.Add(Order);

// Or set the reverse
Order.Customer := Customer;

// Many-to-many: Add to either side
Student.Courses.Add(Course);
// or
Course.Students.Add(Student);

How do I unlink objects?¶

// Remove from list
Customer.Orders.Remove(Order);

// Or set reference to nil
Order.Customer := nil;

How do I navigate associations?¶

// One-to-many
for Order in Customer.Orders do
  ProcessOrder(Order);

// Get parent
var Customer := Order.Customer;

// Chain navigation
for Line in Customer.Orders[0].OrderLines do
  ProcessLine(Line);

Null Values¶

How do I check if an attribute is null?¶

if Customer.M_Email.IsNull then
  ShowMessage('No email address');

How do I set an attribute to null?¶

Customer.M_Email.SetToNull;

How do I handle nulls safely?¶

var Email: string;
if Customer.M_Email.IsNull then
  Email := 'N/A'
else
  Email := Customer.Email;

Transactions¶

How do I use transactions?¶

BoldSystem.StartTransaction;
try
  // Make changes
  Customer.Name := 'New Name';
  Order.Delete;

  BoldSystem.CommitTransaction;
  BoldSystem.UpdateDatabase;
except
  BoldSystem.RollbackTransaction;
  raise;
end;

What happens if I don't use transactions?¶

Changes are still tracked but won't be atomic. Multiple changes could partially save if an error occurs during UpdateDatabase.

UI Binding¶

How do I bind a grid to a list?¶

// Set up list handle
BoldListHandle1.RootHandle := BoldSystemHandle1;
BoldListHandle1.Expression := 'Customer.allInstances';

// Bind grid
BoldGrid1.BoldHandle := BoldListHandle1;

How do I bind an edit to an attribute?¶

BoldEdit1.BoldHandle := CustomerHandle;
BoldEdit1.BoldProperties.Expression := 'name';

Why isn't my UI updating?¶

Check that handles are connected properly
Verify the expression is correct
Ensure object is part of the system
Check that subscriptions are not blocked

Performance¶

// Fetch customers and their orders in fewer queries
BoldSystem.FetchLinksWithObjects(CustomerList, 'orders');

Why are my queries slow?¶

Use batch fetching instead of lazy loading
Add database indexes on frequently queried columns
Use OCL ->select() to filter in database, not in memory
Avoid allInstances on large tables without filtering

How do I reduce memory usage?¶

// Unload objects not currently needed
BoldSystem.Classes['LargeClass'].UnloadAll;

Troubleshooting¶

"Object not found" error¶

The object may have been deleted or not yet saved. Check:

if (Obj <> nil) and (Obj.BoldExistenceState = esExisting) then
  // Safe to use

"Cannot modify read-only object"¶

The object may be from a derived list or unloaded. Ensure you have the actual object from the system.

Database update fails¶

Check for constraint violations
Verify database connection is active
Look for objects with invalid foreign keys
Check for circular dependencies

OCL expression error¶

Verify class and attribute names match the model
Check for typos in navigation paths
Ensure types are compatible in comparisons
Use parentheses to clarify complex expressions

Migration¶

How do I update the database schema?¶

Use Bold's DbEvolutor to generate migration scripts:

BoldDbEvolutor1.GenerateScript;
// Review and execute the generated SQL

Can I use Bold with an existing database?¶

Yes, but you need to:

Create a UML model matching the existing schema.
Create a new database with Bold.
Configure table/column mappings in tagged values.
Import existing data carefully.