Queries

Overview

Midio expressions support a specialized query expression syntax for working with lists of data in a clear, readable, and declarative way.

A query expression is composed of a sequence of clauses that are evaluated top to bottom:

• from introduces a variable that iterates over a collection

• where filters elements based on a condition (optional)

• join combines elements from multiple collections based on a predicate (optional)

• select defines the final shape of the result

At minimum, a query must contain a from clause and a select clause. Additional clauses refine or enrich the data as needed.

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Basic Queries (from / select)

Example 1: Transforming values

Convert each number in a list into a new value.

from n in [1, 2, 3, 4]
select n * 2

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Example 2: Selecting a field from objects

Extract a single field from each object.

from u in [
  { email: "[email protected]" },
  { email: "[email protected]" }
]
select u.email

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Example 3: Constructing new objects

Build a new object for each element in the collection.

from p in [
  { name: "Pen", price: 10 },
  { name: "Notebook", price: 25 }
]
select {
  name: p.name,
  price: p.price
}

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Filtering with where

Example 4: Filtering values

Keep only values that satisfy a condition.

from n in [5, 12, 30]
where n > 10
select n

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Example 5: Filtering objects

Filter objects before selecting a field.

from u in [
  { email: "[email protected]", isActive: true },
  { email: "[email protected]", isActive: false }
]
where u.isActive
select u.email

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Example 6: Filtering and transforming

Filter objects and return a transformed result.

from o in [
  { id: 1, total: 50 },
  { id: 2, total: 200 }
]
where o.total > 100
select {
  id: o.id,
  total: o.total
}

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Joining Collections (join)

Example 7: Simple join

Description: Combine related data from two collections.

from u in [ { id: 1, name: "Alice" } ]
join o in [ { userId: 1, total: 100 } ] 
  on u.id == o.userId
select {
  user: u.name,
  total: o.total
}

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Example 8: Join with filtering

Join data and filter the combined result.

from u in [ { id: 1, name: "Alice" } ]
join o in [ { userId: 1, total: 1000 } ] 
  on u.id == o.userId
where o.total > 500
select {
  user: u.name,
  total: o.total
}

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Example 9: Join with conditions on both sides

Use fields from both collections in the filter.

from u in [ { id: 1, name: "Alice", isActive: true } ]
join o in [ { userId: 1, id: 10, total: 1000 } ] 
  on u.id == o.userId
where u.isActive && o.total > 500
select {
  user: u.name,
  orderId: o.id
}