IDs, Paths, Strings, and Keywords

This article provides reference information for the following:

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Identifiers

Identifiers are the names of collections, documents, fields, and other database objects.

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Rules for Identifiers

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Reserved Identifiers

The following table provides an overview of the DQL-specific restrictions that supersede common identifier rules:

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Path Expressions

Since Ditto stores data as JSON-like documents, you can use keypath indexing, known commonly as dot syntax, to navigate and reference specific parts of a Ditto document when performing query operations in DQL.

To separate a name in a path, use a dot (.).

For example, to navigate to the seats field in a SELECT statement:

SELECT * FROM COLLECTION cars (features MAP)
WHERE features.seats = 'leather'

{
  "_id": "123abc",
  "year": 2018,
  "vin": 123456,
  "features": {
    "speakers": 5
    "seats": "leather"
    }
  }

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Rules for Path Expressions

Following is an overview of the of the DQL-specific restrictions that supersede common rules:

• b is an intermediate name
• c is the rightmost name | | Collections | Collection names cannot be present in path expressions. | | Types | Only REGISTER with nested JSON object and MAP types can be navigated with path expressions. | | MISSING | The path expression result is MISSING for the following conditions are both true:* The leftmost name and all intermediate names are a REGISTER with JSON object type or a MAP type.
• The last name in the path does not exist. |

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String Literals

Enclose string literals in single quotes ('') in DQL; for example 'blue' :

SELECT * FROM cars WHERE color = 'blue'

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Comments

DQL supports both inline and multi-line comments.

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Inline Comments

Inline comments are made using the -- operator.

-- This is an inline comment

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Multi-line Comments

Multi-line comments are inclosed by the /* and */operator.

/*
 This is a multi-line comment
*/

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Reserved Keyword

The following table provides a complete overview of the reserved keywords in DQL: