{"id":2497,"date":"2022-09-24T10:46:18","date_gmt":"2022-09-24T15:46:18","guid":{"rendered":"http:\/\/ninmonkeys.com\/blog\/?p=2497"},"modified":"2024-06-02T00:51:06","modified_gmt":"2024-06-02T05:51:06","slug":"inspecting-function-subtypes-in-power-query","status":"publish","type":"post","link":"https:\/\/ninmonkeys.com\/blog\/2022\/09\/24\/inspecting-function-subtypes-in-power-query\/","title":{"rendered":"Inspecting Function “subtypes” in Power Query"},"content":{"rendered":"\n\n\n

PowerQuery has metadata that you don’t normally see. For example, take the function Table.FromRecords<\/a><\/p>\n\n\n\n

Create a new blank query,<\/strong> and set the value to a function’s name. When you reference a function without arguments or parenthesis, it displays documentation. ( It’s mostly the same as the online docs<\/a> )<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Where does this come from? A lot of it is generated by metadata on the function’s type<\/strong> itself. <\/p>\n\n\n\n

Let’s start drilling down. Using the function Value.Type<\/a> you can view the type’s definition<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

It doesn’t seem very useful at first. The data we want is from the metadata, the Ascribed types<\/a>.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Metadata of the function type<\/h2>\n\n\n\n

The first level describes the function using specific field names that the UI looks for<\/a> . The UI renders some Html from the [Documentation.LongDescription]<\/code> value.<\/p>\n\n\n\n

You can drill down to [Documentation.Examples]<\/code> , which is a list of records. <\/p>\n\n\n\n

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Viewing Documenation.Examples<\/code><\/figcaption><\/figure>\n\n\n\n

Function Parameters Types<\/h2>\n\n\n\n

There can be data defined for the arguments themselves. Parameters that are type any<\/code> may have more information in their metadata<\/a>. <\/p>\n\n\n\n

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Parameters may have metadata<\/figcaption><\/figure>\n\n\n\n
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Sometimes the metadata, of a parameter’s metadata — has more metadata! <\/figcaption><\/figure>\n\n\n\n

Your First Function types<\/h2>\n\n\n\n

How do you document your own functions? Here’s a medium example. The function declared further below starts with this definition:<\/p>\n\n\n\n

Text.ReplacePartialMatches_impl = (\n        source as text, mapping as table\n    ) as text => ...<\/code><\/pre>\n\n\n\n
To create the type, you start your function type<\/code> almost the exact same as the definition. Then wrap it inside a type function<\/code> <\/p>\n\n\n\n
Text.ReplacePartialMatches.Type = type function(\n        source as text,\n        mapping as table\n    ) as text meta [ .. ]<\/code><\/pre>\n\n\n\n
Next you start adding records to the final type’s metadata. If you haven’t seen the meta<\/code> operator, check out Ben’s series:<\/p>\n\n\n\n
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Power Query M Primer (Part 20): Metadata<\/a><\/blockquote>