Validation

Trysil provides attribute-based validation for entity fields. Validation attributes are defined in Trysil.Validation.Attributes.pas and the error collection infrastructure is in Trysil.Validation.pas.

Validation Attributes

Decorate entity fields with one or more validation attributes:

Attribute	Description	Example
TRequired	Field cannot be empty, null, or zero	[TRequired]
TMaxLength(n)	Maximum string length	[TMaxLength(50)]
TMinLength(n)	Minimum string length	[TMinLength(3)]
TMaxValue(n)	Maximum numeric value (Integer or Double)	[TMaxValue(100)]
TMinValue(n)	Minimum numeric value (Integer or Double)	[TMinValue(0)]
TGreater(n)	Must be strictly greater than n	[TGreater(0)]
TLess(n)	Must be strictly less than n	[TLess(1000)]
TRange(min, max)	Value must be within range (inclusive)	[TRange(1, 100)]
TRegex(pattern)	Must match a regular expression	[TRegex('^[A-Z]')]
TEmail	Must be a valid email address	[TEmail]
TDisplayName(name)	Human-readable field name for error messages	[TDisplayName('First Name')]

Example

[TTable('Persons')]
[TSequence('PersonsID')]
TPerson = class
strict private
  [TPrimaryKey]
  [TColumn('ID')]
  FID: TTPrimaryKey;

  [TRequired]
  [TMaxLength(100)]
  [TDisplayName('First Name')]
  [TColumn('Firstname')]
  FFirstname: String;

  [TRequired]
  [TMaxLength(100)]
  [TColumn('Lastname')]
  FLastname: String;

  [TMaxLength(255)]
  [TEmail]
  [TColumn('Email')]
  FEmail: String;

  [TMinValue(0)]
  [TMaxValue(150)]
  [TColumn('Age')]
  FAge: Integer;

  [TVersionColumn]
  [TColumn('VersionID')]
  FVersionID: TTVersion;
public
  property ID: TTPrimaryKey read FID;
  property Firstname: String read FFirstname write FFirstname;
  property Lastname: String read FLastname write FLastname;
  property Email: String read FEmail write FEmail;
  property Age: Integer read FAge write FAge;
end;

Custom Error Messages

All validation attributes accept an optional error message parameter. When omitted, a default message is generated using the column name:

[TRequired('Firstname is mandatory')]
[TMaxLength(50, 'Name must be 50 characters or fewer')]
[TEmail('Please enter a valid email address')]
[TRange(1, 100, 'Value must be between 1 and 100')]

TRequired Behavior

TRequired validates different types as follows:

• String: fails if the value is empty ('')
• TDateTime: fails if the value is zero (0)
• TTNullable\<T>: fails if the nullable is in null state
• TTLazy\<T> (object): fails if the referenced entity is nil

Explicit Validation

Call Validate<T> on the context to check an entity before submitting. If validation fails, ETValidationException is raised:

try
  LContext.Validate<TPerson>(LPerson);
except
  on E: ETValidationException do
    ShowMessage(E.Message);
end;

TTValidationErrors

Validation errors are collected in a TTValidationErrors instance. Each error is a TTValidationError record containing:

• ColumnName -- the field/column that failed validation
• ErrorMessage -- the human-readable error description

Formatting Errors

// Human-readable text (one line per error)
LErrors.ToString;
// Example output:
// - Firstname: First Name is required.
// - Email: Invalid email address.

// JSON format (for APIs)
LErrors.ToJSon;
// Example output:
// [{"columnName":"Firstname","errorMessage":"First Name is required."},
//  {"columnName":"Email","errorMessage":"Invalid email address."}]

Checking for Errors

if not LErrors.IsEmpty then
  ShowMessage(LErrors.ToString);

Automatic Validation

Validation runs automatically before every Insert and Update operation inside the resolver. You do not need to call Validate manually unless you want to check the entity before submitting -- for example, to display errors in a UI before the user confirms the save.

Custom Validators

For validation logic that cannot be expressed with attributes, use event method attributes directly on the entity class:

TPerson = class
strict private
  // fields...

  [TBeforeInsert]
  procedure ValidateOnInsert;

  [TBeforeUpdate]
  procedure ValidateOnUpdate;
end;

procedure TPerson.ValidateOnInsert;
begin
  if FFirstname = FLastname then
    raise ETException.Create('Firstname and Lastname cannot be the same');
end;

procedure TPerson.ValidateOnUpdate;
begin
  ValidateOnInsert; // reuse the same logic
end;

These methods are called by the resolver during the event lifecycle, after attribute-based validation has passed. See Events for the full lifecycle.