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Validation Flow

Understanding how validation works in Seal from input to output.

Architecture First

This page covers the validation process. For the complete architecture overview, see Three-Layer Architecture.

Overview​

Seal validation follows a specific flow:

  1. Input → Raw data
  2. Mutators → Transform data
  3. Validators → Check data
  4. Output → Validation result

Basic Flow Example​

// Input: "  USER@EXAMPLE.COM  "
const result = await v.validate(
  v.string().trim().lowercase().email().maxLength(100),
  "  USER@EXAMPLE.COM  "
);

// Output: { isValid: true, data: "user@example.com", errors: [] }

Validation Result Structure​

interface ValidationResult {
  isValid: boolean;
  data: any; // The validated (and potentially mutated) data
  errors: ValidationError[]; // Array of validation errors
}

interface ValidationError {
  type: string; // The rule that failed
  error: string; // The error message
  input: string; // The field path that failed
}

Error Handling​

Single Error Mode​

const config = { firstErrorOnly: true };
const result = await validate(schema, data, config);

// Returns only the first error found
{
  isValid: false,
  errors: [{
    type: "minLength",
    error: "The :input must be at least 5 characters",
    input: "hi"
  }],
  data: "hi"
}

Multiple Errors Mode​

const config = { firstErrorOnly: false };
const result = await validate(schema, data, config);

// Returns all validation errors
{
  isValid: false,
  errors: [
    { type: "minLength", error: "...", input: "hi123" },
    { type: "alpha", error: "...", input: "hi123" }
  ],
  data: "hi123"
}

Performance Considerations​

Early Exit​

// ✅ Good: Check required fields first
v.string()
  .required()       // Check first
  .email()          // Then format
  .maxLength(100)   // Then length

Efficient Order​

// ✅ Good: Mutators before validators
v.string()
  .trim()           // Clean first
  .lowercase()      // Normalize
  .email()          // Then validate

See Also​