# `Dose`

An amount of a medicine, by mass or by volume, above nothing. Shown in milligrams or millilitres: `500 mg`, `5 ml`.

[Health](types.md#health); not ordered; since Jadpo 0.1.0.

## Make one

Pick one of its variants and give its fields, `Dose.mass { amount: ... }`.

## Variants

| Variant | Fields |
|---|---|
| `mass` | `amount`: [`Mass`](type-mass.md) |
| `volume` | `amount`: [`Volume`](type-volume.md) |

## Text, JSON and storage

It has no single text form, so `text.from` and `text.parse` don't take it. JSON sends an object of its variant's name, as `tag`, and the variant's fields.

| JSON |
|---|
| `{"tag":"mass","amount":{"value":"0.0005","unit":"kg"}}` |
| `{"tag":"mass","amount":{"value":"0.000000125","unit":"kg"}}` |
| `{"tag":"mass","amount":{"value":"0.001","unit":"kg"}}` |
| `{"tag":"volume","amount":{"value":"0.000005","unit":"cubic_metre"}}` |

It is stored in 2 columns, each named for the field, `_` and its suffix. This is `{"tag":"mass","amount":{"value":"0.001","unit":"kg"}}`:

| Column | Type | Holds |
|---|---|---|
| `<field>_kind` | `text` | `'mass'` |
| `<field>_amount` | `numeric(38, 9)` | `0.001` |

## Shown to people

`text.format(value, locale:)` shows it to people in their locale.

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `{"tag":"mass","amount":{"value":"500","unit":"mg"}}` | `500 mg` |
| `{"tag":"mass","amount":{"value":"125","unit":"mcg"}}` | `0.125 mg` |
| `{"tag":"mass","amount":{"value":"1","unit":"g"}}` | `1,000 mg` |
| `{"tag":"volume","amount":{"value":"5","unit":"ml"}}` | `5 ml` |

## Operations

It has the contract's own operations: `text.format`, `json.read`, `json.write` and `==`. It isn't ordered, so `<` and sorting don't take it. [Every standard type meets one contract](../topics/every-standard-type-meets-one-contract.md) says how they work.