tag-query 1.0.0

A Python package for robust querying of string lists in MongoDB.

A DSL for robust querying of tags in MongoDB

This module converts a text query into a dict that can be directly used in a MongoDB query of a string array field.

To get started, include this repo as a submodule in your project. Then you can use it directly. For example, to query a collection for any documents for which the field field_name contains value1 and value2:

from tag_query import compile_query, exceptions

try:
  mongo_query = compile_query(
    expression = 'value1 and value2',
    field = 'field_name'
  )
  # Or just `compile_query('value1 and value2', 'field_name')`
except exceptions.ParseError as e:
  print(e)
  exit(1)

print(mongo_query) #will output -> {'$and': [{'field_name': 'value1'}, {'field_name': 'value2'}]}

---

Syntax

First, it's important to note that a tag query expression has no precedence; expressions are evaluated from left to right, unless otherwise demarcated by parentheses.

• TAG: case-sensitive
  • simple: Any non-keyword, non-function, alphanumeric text. some_tag and ThisIsATag123 both count.
  • quoted: Any string of text inside double quotes. "tag-with-dashes and operator text" is a single tag.
  • regex: Any string inside curly braces. {^[A-Za-z0-9]+$} matches any purely alphanumeric tag.
  • CAVEATS for simple and quoted tags:
    • If placed next to each other without an operator between them, the tags will concatenate with a single space as the delimiter. E.g. tag1 and tag2 tag3 is the same as "tag1" and "tag2 tag3"
    • The Glob operator (*) may be used for simple pattern matching. E.g. *test* will match any tag that begins or ends with "test", such as "contested". *test or test* are also valid, and match tags that end and begin with "test", respectively.
• OPERATOR: case-insensitive
  • and, +: Require both values to exist. tag1 and tag2 or tag1 + tag2
  • or, /: Require at least 1 value to exist. tag1 or tag2 or tag1 / tag2
  • not, -: Invert the selection. not tag1 or not (tag1 and tag2)
    • In a binary expression, not can equal and not. For example tag1 not tag2 or tag1 - tag2
• FUNCTION: case-insensitive
  • eq,equals,exact,exactly, =: Require the document to have exactly that many tags. exactly 5
  • lt,fewer,below, <: Require the document to have fewer than that many tags. fewer 5
  • gt,greater,above, >: Require the document to have more than that many tags. greater 5
  • le,max,maximum, <=: Require the document to have at most that many tags. maximum 5
  • ge,min,minimum, >=: Require the document to have at least that many tags. minimum 5
• PARENTHESES:
  • (, ): Controls order of operations. a + (b - c) is different from (a + b) - c (the latter is the same as a + b - c. remember: left to right).

---

Examples

Here are some example tag queries and their corresponding outputs. The outputs can be directly passed to MongoDB as selection criteria.

Query Expression	MongoDB Query Output
tag1 and tag2	{'$and': [{'field_name': 'tag1'}, {'field_name': 'tag2'}]}
tag1 or tag2	{'$or': [{'field_name': 'tag1'}, {'field_name': 'tag2'}]}
not tag1	{'field_name': {'$ne': 'tag1'}}
tag1 and not tag2	{'$and': [{'field_name': 'tag1'}, {'field_name': {'$ne': 'tag2'}}]}
"tag with spaces"	{'field_name': 'tag with spaces'}
three tags concatenated	{'field_name': 'three tags concatenated'}
{^foo.*}	{'field_name': {'$regex': '^foo.*'}}
*test*	{'field_name': {'$regex': 'test'}}
exactly 3	{'tags': {'$size': 3}}
fewer 2	{'tags.1': {'$exists': False}}
minimum 5	{'tags.4': {'$exists': True}}
tag1 or (tag2 and not tag3)	{'$or': [{'field_name': 'tag1'}, {'$and': [{'field_name': 'tag2'}, {'field_name': {'$ne': 'tag3'}}]}]}

You can use any of these expressions with compile_query(expression, field='field_name').