0a4a5b36cc
* Additional .gitignore entries * Merge a bunch of small articles about system tables into single one * Merge a bunch of small articles about formats into single one * Adapt table with formats to English docs too * Add SPb meetup link to main page * Move Utilities out of top level of docs (the location is probably not yet final) + translate couple articles * Merge MacOS.md into build_osx.md * Move Data types higher in ToC * Publish changelog on website alongside documentation * Few fixes for en/table_engines/file.md * Use smaller header sizes in changelogs * Group up table engines inside ToC * Move table engines out of top level too * Specificy in ToC that query language is SQL based. Thats a bit excessive, but catches eye. * Move stuff that is part of query language into respective folder * Move table functions lower in ToC * Lost redirects.txt update * Do not rely on comments in yaml + fix few ru titles * Extract major parts of queries.md into separate articles * queries.md has been supposed to be removed * Fix weird translation * Fix a bunch of links * There is only table of contents left * "Query language" is actually part of SQL abbreviation * Change filename in README.md too * fix mistype
2.3 KiB
Functions for working with JSON
In Yandex.Metrica, JSON is transmitted by users as session parameters. There are some special functions for working with this JSON. (Although in most of the cases, the JSONs are additionally pre-processed, and the resulting values are put in separate columns in their processed format.) All these functions are based on strong assumptions about what the JSON can be, but they try to do as little as possible to get the job done.
The following assumptions are made:
- The field name (function argument) must be a constant.
- The field name is somehow canonically encoded in JSON. For example:
visitParamHas('{"abc":"def"}', 'abc') = 1, butvisitParamHas('{"\\u0061\\u0062\\u0063":"def"}', 'abc') = 0 - Fields are searched for on any nesting level, indiscriminately. If there are multiple matching fields, the first occurrence is used.
- The JSON doesn't have space characters outside of string literals.
visitParamHas(params, name)
Checks whether there is a field with the 'name' name.
visitParamExtractUInt(params, name)
Parses UInt64 from the value of the field named 'name'. If this is a string field, it tries to parse a number from the beginning of the string. If the field doesn't exist, or it exists but doesn't contain a number, it returns 0.
visitParamExtractInt(params, name)
The same as for Int64.
visitParamExtractFloat(params, name)
The same as for Float64.
visitParamExtractBool(params, name)
Parses a true/false value. The result is UInt8.
visitParamExtractRaw(params, name)
Returns the value of a field, including separators.
Examples:
visitParamExtractRaw('{"abc":"\\n\\u0000"}', 'abc') = '"\\n\\u0000"'
visitParamExtractRaw('{"abc":{"def":[1,2,3]}}', 'abc') = '{"def":[1,2,3]}'
visitParamExtractString(params, name)
Parses the string in double quotes. The value is unescaped. If unescaping failed, it returns an empty string.
Examples:
visitParamExtractString('{"abc":"\\n\\u0000"}', 'abc') = '\n\0'
visitParamExtractString('{"abc":"\\u263a"}', 'abc') = '☺'
visitParamExtractString('{"abc":"\\u263"}', 'abc') = ''
visitParamExtractString('{"abc":"hello}', 'abc') = ''
There is currently no support for code points in the format \uXXXX\uYYYY that are not from the basic multilingual plane (they are converted to CESU-8 instead of UTF-8).