Misc

The misc section allows you to inject arbitrary Go code into the generated package. Use it to define constants, custom types, and helper functions that your generators can reuse.

Model

Create a file named Product.dg:

Product.dg

model Product {
  misc {
    // Constants for configuration
    const MinPrice = 10.0
    const MaxPrice = 500.0
    const TaxRate = 0.08

    // Custom type for product categories
    type Category string

    const (
      Electronics Category = "Electronics"
      Clothing    Category = "Clothing"
      Books       Category = "Books"
      Home        Category = "Home"
    )

    // Helper function to generate SKU
    func generateSKU(category Category, id int) string {
      prefix := ""
      switch category {
        case Electronics: prefix = "ELEC"
        case Clothing:    prefix = "CLTH"
        case Books:       prefix = "BOOK"
        case Home:        prefix = "HOME"
      }
      return fmt.Sprintf("%s-%08d", prefix, id)
    }
  }

  fields {
    id() int
    name() string
    category() string
    sku() string
    price() float64
    price_with_tax() float64
  }

  gens {
    func id() {
      return iter + 1
    }

    func name() {
      return fmt.Sprintf("Product %d", iter+1)
    }

    func category() {
      categories := []Category{Electronics, Clothing, Books, Home}
      return string(categories[iter%4])
    }

    func sku() {
      cat := Category(self.category(iter))
      return generateSKU(cat, self.id(iter))
    }

    func price() {
      return FloatBetween(MinPrice, MaxPrice)
    }

    func price_with_tax() {
      basePrice := self.price(iter)
      return basePrice * (1.0 + TaxRate)
    }
  }
}

Usage Highlights

• Constants: MinPrice, MaxPrice, TaxRate for configuration values
• Custom Types: Category type with predefined values
• Helper Functions: generateSKU() to create product codes
• Using misc in gens: All constants, types, and functions are accessible in generation logic

How to Run

$ datagenc gen . -n 10

Output

Product{id:1 name:Product 1 category:Electronics sku:ELEC-00000001 price:341.25 price_with_tax:368.55}
Product{id:2 name:Product 2 category:Clothing sku:CLTH-00000002 price:127.83 price_with_tax:138.06}
Product{id:3 name:Product 3 category:Books sku:BOOK-00000003 price:89.45 price_with_tax:96.61}
Product{id:4 name:Product 4 category:Home sku:HOME-00000004 price:234.67 price_with_tax:253.44}
Product{id:5 name:Product 5 category:Electronics sku:ELEC-00000005 price:456.12 price_with_tax:492.61}
Product{id:6 name:Product 6 category:Clothing sku:CLTH-00000006 price:78.90 price_with_tax:85.21}
Product{id:7 name:Product 7 category:Books sku:BOOK-00000007 price:145.23 price_with_tax:156.85}
Product{id:8 name:Product 8 category:Home sku:HOME-00000008 price:312.45 price_with_tax:337.45}
Product{id:9 name:Product 9 category:Electronics sku:ELEC-00000009 price:198.76 price_with_tax:214.66}
Product{id:10 name:Product 10 category:Clothing sku:CLTH-00000010 price:267.34 price_with_tax:288.73}

Key Benefits

• Reusability: Define once, use across multiple fields
• Type Safety: Use Go’s type system for better code quality
• Organization: Keep related constants and helpers together
• Maintainability: Change configuration values in one place