Tarantool tuples converter in Go

Table of contents

• Documentation
  • Converter
  • Mapper
  • Mappers to tarantool types
    • Example
    • String to nullable
    • String to any/scalar
    • Customization

Documentation

Converter

Converter[S,T] converts objects of type S into objects of type T. Converters are basic entities on which mappers are based.
Implementations of some converters are available, for example, converters from strings to golang types.
Usage example:

// Basic converter.
strToBoolConv := tupleconv.MakeStringToBoolConverter()
result, err := strToBoolConv.Convert("true") // true <nil>

// Function based converter.
funcConv := tupleconv.MakeFuncConverter(func(s string) (string, error) {
    return s + " world!", nil
})
result, err = funcConv.Convert("hello") // hello world! <nil>

Note 1: You can use the provided converters.

Note 2: You can create your own converters based on the functions with tupleconv.MakeFuncConverter.

Note 3: You can create your own converters, implementing Converter[S,T] interface.

Mapper

Mapper is an object that converts tuples. It is built using a list of converters.
Usage example:

// Mapper example.
mapper := tupleconv.MakeMapper[string, any]([]tupleconv.Converter[string, any]{
    tupleconv.MakeFuncConverter(func(s string) (any, error) {
        return s + "1", nil
    }),
    tupleconv.MakeFuncConverter(func(s string) (any, error) {
        iVal, err := strconv.Atoi(s)
        if err != nil {
            return nil, errors.New("can't convert")
        }
	return iVal + 1, nil
    }),
})
result, err := mapper.Map([]string{"a", "4"}) // []any{"a1", 5} <nil>
result, err = mapper.Map([]string{"0"}) // []any{"01"} <nil>

// Single mapper example.
toStringMapper := tupleconv.MakeMapper([]tupleconv.Converter[any, string]{}).
        WithDefaultConverter(tupleconv.MakeFuncConverter(
            func(s any) (string, error) {
                return fmt.Sprintln(s), nil
        }),
)
res, err := toStringMapper.Map([]any{1, 2.5, nil}) // ["1\n", "2.5\n", "<nil>\n"] <nil>

Note 1: To create a mapper, an array of converters is needed, each of which transforms a certain type S into type T.

Note 2: To perform tuple mapping, you can use the function Map, which will return control to the calling code upon the first error.

Note 3: You can set a default converter that will be applied if the tuple length exceeds the size of the primary converters list.
For example, if you only set a default converter, Map will work like the map function in functional programming languages.

Note 4: If tuple length is less than converters list length, then only corresponding converters will be applied.

Mappers to tarantool types

Example

For building an array of converters, especially when it comes to conversions to tarantool types, there is a built-in solution.
Let's consider an example:

factory := tupleconv.MakeStringToTTConvFactory().
                WithDecimalSeparators(",.")

spaceFmt := []tupleconv.SpaceField{
    {Type: tupleconv.TypeUnsigned},
    {Type: tupleconv.TypeDouble, IsNullable: true},
    {Type: tupleconv.TypeString},
}

converters, _ := tupleconv.MakeTypeToTTConverters[string](factory, spaceFmt)
mapper := tupleconv.MakeMapper(converters)
result, err := mapper.Map([]string{"1", "-2,2", "some_string"}) // [1, -2.2, "some_string"] <nil>

Note 1: To build an array of converters, the space format and a certain object implementing TTConvFactory are used. Function MakeTypeToTTConverters takes these entities and gives the converters list.

Note 2: TTConvFactory[Type] is capable of building a converter from Type to each tarantool type.

Note 3: There is a basic factory available called StringToTTConvFactory, which is used for conversions from strings to tarantool types.

Note 4: StringToTTConvFactory can be configured with options like WithDecimalSeparators.

String to nullable

When converting nullable types with StringToTTConvFactory, first, an attempt is made to convert to null.

For example, empty string is interpreted like null with default options. If a field has a string type and is nullable, then an empty string will be converted to null during the conversion process, rather than being converted to empty string.

String to any/scalar

When converting to any/scalar with StringToTTConvFactory, by default, an attempt will be made to convert them to the following types, in the following order:

• number
• decimal
• boolean
• datetime
• uuid
• interval
• string

Customization

TTConvFactory[Type] is an interface that can build a mapper from Type to each tarantool type.
To customize the behavior for specific types, one can inherit from the existing factory and override the necessary methods.
For example, let's make the standard factory for conversion from strings to tarantool types always convert any type to a string:

type customFactory struct {
    tupleconv.StringToTTConvFactory
}

func (f *customFactory) MakeTypeToAnyMapper() tupleconv.Converter[string, any] {
    return tupleconv.MakeFuncConverter(func(s string) (any, error) {
        return s, nil
    })
}

func example() {
    factory := &customFactory{}
    spaceFmt := []tupleconv.SpaceField{{Type: "any"}}
    converters, _ := tupleconv.MakeTypeToTTConverters[string](factory, spaceFmt)

    res, err := converters[0].Convert("12") // "12" <nil>
}