tableschema-pr-118
v1.4.2-alpha1
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A library for working with Table Schema in Javascript.
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tableschema-js
A library for working with Table Schema.
Version v1.0 includes various important changes. Please read a migration guide.
Features
Table
class for working with data and schemaSchema
class for working with schemasField
class for working with schema fieldsvalidate
function for validating schema descriptorsinfer
function that creates a schema based on a data sample
Getting started
Installation
The package use semantic versioning. It means that major versions could include breaking changes. It's highly recommended to specify tableschema
version range in your package.json
file e.g. tabulator: ^1.0
which will be added by default by npm install --save
.
NPM
$ npm install jsontableschema # v0.2
$ npm install tableschema@latest # v1.0-alpha
CDN
<script src="//unpkg.com/tableschema/dist/tableschema.min.js"></script>
Examples
Code examples in this readme requires Node v8.3+ or proper modern browser . Also you have to wrap code into async function if there is await keyword used. You could see even more example in examples directory.
const {Table} = require('tableschema')
const table = await Table.load('data.csv')
await table.infer() // infer a schema
await table.read({keyed: true}) // read the data
await table.schema.save() // save the schema
await table.save() // save the data
Documentation
Table
A table is a core concept in a tabular data world. It represents a data with a metadata (Table Schema). Let's see how we could use it in practice.
Consider we have some local csv file. It could be inline data or remote link - all supported by Table
class (except local files for in-brower usage of course). But say it's data.csv
for now:
city,location
london,"51.50,-0.11"
paris,"48.85,2.30"
rome,N/A
Let's create and read a table. We use static Table.load
method and table.read
method with a keyed
option to get array of keyed rows:
const table = await Table.load('data.csv')
table.headers // ['city', 'location']
await table.read({keyed: true})
// [
// {city: 'london', location: '51.50,-0.11'},
// {city: 'paris', location: '48.85,2.30'},
// {city: 'rome', location: 'N/A'},
// ]
As we could see our locations are just a strings. But it should be geopoints. Also Rome's location is not available but it's also just a N/A
string instead of JavaScript null
. First we have to infer Table Schema:
await table.infer()
table.schema.descriptor
// { fields:
// [ { name: 'city', type: 'string', format: 'default' },
// { name: 'location', type: 'geopoint', format: 'default' } ],
// missingValues: [ '' ] }
await table.read({keyed: true})
// Fails with a data validation error
Let's fix not available location. There is a missingValues
property in Table Schema specification. As a first try we set missingValues
to N/A
in table.schema.descriptor
. Schema descriptor could be changed in-place but all changes sould be commited by table.schema.commit()
:
table.schema.descriptor['missingValues'] = 'N/A'
table.schema.commit()
table.schema.valid // false
table.schema.errors
// Error: Descriptor validation error:
// Invalid type: string (expected array)
// at "/missingValues" in descriptor and
// at "/properties/missingValues/type" in profile
As a good citiziens we've decided to check out schema descriptor validity. And it's not valid! We sould use an array for missingValues
property. Also don't forget to have an empty string as a missing value:
table.schema.descriptor['missingValues'] = ['', 'N/A']
table.schema.commit()
table.schema.valid // true
All good. It looks like we're ready to read our data again:
await table.read({keyed: true})
// [
// {city: 'london', location: [51.50,-0.11]},
// {city: 'paris', location: [48.85,2.30]},
// {city: 'rome', location: null},
// ]
Now we see that:
- locations are arrays with numeric lattide and longitude
- Rome's location is a native JavaScript
null
And because there are no errors on data reading we could be sure that our data is valid againt our schema. Let's save it:
await table.schema.save('schema.json')
await table.save('data.csv')
Our data.csv
looks the same because it has been stringified back to csv
format. But now we have schema.json
:
{
"fields": [
{
"name": "city",
"type": "string",
"format": "default"
},
{
"name": "location",
"type": "geopoint",
"format": "default"
}
],
"missingValues": [
"",
"N/A"
]
}
If we decide to improve it even more we could update the schema file and then open it again. But now providing a schema path and iterating thru the data using Node Streams:
const table = await Table.load('data.csv', {schema: 'schema.json'})
const stream = await table.iter({stream: true})
stream.on('data', (row) => {
// handle row ['london', [51.50,-0.11]] etc
// keyed/extended/cast supported in a stream mode too
})
It was onle basic introduction to the Table
class. To learn more let's take a look on Table
class API reference.
async Table.load(source, {schema, strict=false, headers=1, ...parserOptions})
Factory method to instantiate Table
class. This method is async and it should be used with await keyword or as a Promise
. If references
argument is provided foreign keys will be checked on any reading operation.
source (String/Array[]/Stream/Function)
- data source (one of):- local CSV file (path)
- remote CSV file (url)
- array of arrays representing the rows
- readable stream with CSV file contents
- function returning readable stream with CSV file contents
schema (Object)
- data schema in all forms supported bySchema
classstrict (Boolean)
- strictness option to pass toSchema
constructorheaders (Integer/String[])
- data source headers (one of):- row number containing headers (
source
should contain headers rows) - array of headers (
source
should NOT contain headers rows)
- row number containing headers (
parserOptions (Object)
- options to be used by CSV parser. All options listed at http://csv.adaltas.com/parse/#parser-options. By defaultltrim
is true according to the CSV Dialect spec.(errors.TableSchemaError)
- raises any error occured in table creation process(Table)
- returns data table class instance
table.headers
(String[])
- returns data source headers
table.schema
(Schema)
- returns schema class instance
async table.iter({keyed, extended, cast=true, relations=false, stream=false})
Iter through the table data and emits rows cast based on table schema (async for loop). With a stream
flag instead of async iterator a Node stream will be returned. Data casting could be disabled.
keyed (Boolean)
- iter keyed rowsextended (Boolean)
- iter extended rowscast (Boolean)
- disable data casting if falserelations (Object)
- object of foreign key references in a form of{resource1: [{field1: value1, field2: value2}, ...], ...}
. If provided foreign key fields will checked and resolved to its referencesstream (Boolean)
- return Node Readable Stream of table rows(errors.TableSchemaError)
- raises any error occured in this process(AsyncIterator/Stream)
- async iterator/stream of rows:[value1, value2]
- base{header1: value1, header2: value2}
- keyed[rowNumber, [header1, header2], [value1, value2]]
- extended
async table.read({keyed, extended, cast=true, relations=false, limit})
Read the whole table and returns as array of rows. Count of rows could be limited.
keyed (Boolean)
- flag to emit keyed rowsextended (Boolean)
- flag to emit extended rowscast (Boolean)
- disable data casting if falserelations (Object)
- object of foreign key references in a form of{resource1: [{field1: value1, field2: value2}, ...], ...}
. If provided foreign key fields will checked and resolved to its referenceslimit (Number)
- integer limit of rows to return(errors.TableSchemaError)
- raises any error occured in this process(Array[])
- returns array of rows (seetable.iter
)
async table.infer({limit=100})
Infer a schema for the table. It will infer and set Table Schema to table.schema
based on table data.
limit (Number)
- limit rows samle size(Object)
- returns Table Schema descriptor
async table.save(target)
Save data source to file locally in CSV format with ,
(comma) delimiter
target (String)
- path where to save a table data(errors.TableSchemaError)
- raises an error if there is saving problem(Boolean)
- returns true on success
Schema
A model of a schema with helpful methods for working with the schema and supported data. Schema instances can be initialized with a schema source as a url to a JSON file or a JSON object. The schema is initially validated (see validate below). By default validation errors will be stored in schema.errors
but in a strict mode it will be instantly raised.
Let's create a blank schema. It's not valid because descriptor.fields
property is required by the Table Schema specification:
const schema = await Schema.load({})
schema.valid // false
schema.errors
// Error: Descriptor validation error:
// Missing required property: fields
// at "" in descriptor and
// at "/required/0" in profile
To do not create a schema descriptor by hands we will use a schema.infer
method to infer the descriptor from given data:
schema.infer([
['id', 'age', 'name'],
['1','39','Paul'],
['2','23','Jimmy'],
['3','36','Jane'],
['4','28','Judy'],
])
schema.valid // true
schema.descriptor
//{ fields:
// [ { name: 'id', type: 'integer', format: 'default' },
// { name: 'age', type: 'integer', format: 'default' },
// { name: 'name', type: 'string', format: 'default' } ],
// missingValues: [ '' ] }
Now we have an inferred schema and it's valid. We could cast data row against our schema. We provide a string input by an output will be cast correspondingly:
schema.castRow(['5', '66', 'Sam'])
// [ 5, 66, 'Sam' ]
But if we try provide some missing value to age
field cast will fail because for now only one possible missing value is an empty string. Let's update our schema:
schema.castRow(['6', 'N/A', 'Walt'])
// Cast error
schema.descriptor.missingValues = ['', 'N/A']
schema.commit()
schema.castRow(['6', 'N/A', 'Walt'])
// [ 6, null, 'Walt' ]
We could save the schema to a local file. And we could continue the work in any time just loading it from the local file:
await schema.save('schema.json')
const schema = await Schema.load('schema.json')
It was onle basic introduction to the Schema
class. To learn more let's take a look on Schema
class API reference.
async Schema.load(descriptor, {strict=false})
Factory method to instantiate Schema
class. This method is async and it should be used with await keyword or as a Promise
.
descriptor (String/Object)
- schema descriptor:- local path
- remote url
- object
strict (Boolean)
- flag to alter validation behaviour:- if false error will not be raised and all error will be collected in
schema.errors
- if strict is true any validation error will be raised immediately
- if false error will not be raised and all error will be collected in
(errors.TableSchemaError)
- raises any error occured in the process(Schema)
- returns schema class instance
schema.valid
(Boolean)
- returns validation status. It always true in strict mode.
schema.errors
(Error[])
- returns validation errors. It always empty in strict mode.
schema.descriptor
(Object)
- returns schema descriptor
schema.primaryKey
(str[])
- returns schema primary key
schema.foreignKeys
(Object[])
- returns schema foreign keys
schema.fields
(Field[])
- returns an array ofField
instances.
schema.fieldNames
(String[])
- returns an array of field names.
schema.getField(name)
Get schema field by name.
name (String)
- schema field name(Field/null)
- returnsField
instance or null if not found
schema.addField(descriptor)
Add new field to schema. The schema descriptor will be validated with newly added field descriptor.
descriptor (Object)
- field descriptor(errors.TableSchemaError)
- raises any error occured in the process(Field/null)
- returns addedField
instance or null if not added
schema.removeField(name)
Remove field resource by name. The schema descriptor will be validated after field descriptor removal.
name (String)
- schema field name(errors.TableSchemaError)
- raises any error occured in the process(Field/null)
- returns removedField
instances or null if not found
schema.castRow(row)
Cast row based on field types and formats.
row (any[])
- data row as an array of values(any[])
- returns cast data row
schema.infer(rows, {headers=1})
Infer and set schema.descriptor
based on data sample.
rows (Array[])
- array of arrays representing rows.headers (Integer/String[])
- data sample headers (one of):- row number containing headers (
rows
should contain headers rows) - array of headers (
rows
should NOT contain headers rows)
- row number containing headers (
{Object}
- returns Table Schema descriptor
schema.commit({strict})
Update schema instance if there are in-place changes in the descriptor.
strict (Boolean)
- alterstrict
mode for further work(errors.TableSchemaError)
- raises any error occured in the process(Boolean)
- returns true on success and false if not modified
const descriptor = {fields: [{name: 'field', type: 'string'}]}
const schema = await Schema.load(descriptor)
schema.getField('name').type // string
schema.descriptor.fields[0].type = 'number'
schema.getField('name').type // string
schema.commit()
schema.getField('name').type // number
async schema.save(target)
Save schema descriptor to target destination.
target (String)
- path where to save a descriptor(errors.TableSchemaError)
- raises any error occured in the process(Boolean)
- returns true on success
Field
Class represents field in the schema.
Data values can be cast to native Javascript types. Casting a value will check the value is of the expected type, is in the correct format, and complies with any constraints imposed by a schema.
{
'name': 'birthday',
'type': 'date',
'format': 'default',
'constraints': {
'required': True,
'minimum': '2015-05-30'
}
}
Following code will not raise the exception, despite the fact our date is less than minimum constraints in the field, because we do not check constraints of the field descriptor
var dateType = field.castValue('2014-05-29')
And following example will raise exception, because we set flag 'skip constraints' to false
, and our date is less than allowed by minimum
constraints of the field. Exception will be raised as well in situation of trying to cast non-date format values, or empty values
try {
var dateType = field.castValue('2014-05-29', false)
} catch(e) {
// uh oh, something went wrong
}
Values that can't be cast will raise an Error
exception.
Casting a value that doesn't meet the constraints will raise an Error
exception.
Available types, formats and resultant value of the cast:
| Type | Formats | Casting result | | ---- | ------- | -------------- | | any | default | Any | | array | default | Array | | boolean | default | Boolean | | date | default, any, | Date | | datetime | default, any, | Date | | duration | default | moment.Duration | | geojson | default, topojson | Object | | geopoint | default, array, object | [Number, Number] | | integer | default | Number | | number | default | Number | | object | default | Object | | string | default, uri, email, binary | String | | time | default, any, | Date | | year | default | Number | | yearmonth | default | [Number, Number] |
new Field(descriptor, {missingValues=['']})
Constructor to instantiate Field
class.
descriptor (Object)
- schema field descriptormissingValues (String[])
- an array with string representing missing values(errors.TableSchemaError)
- raises any error occured in the process(Field)
- returns field class instance
field.name
(String)
- returns field name
field.type
(String)
- returns field type
field.format
(String)
- returns field format
field.required
(Boolean)
- returns true if field is required
field.constraints
(Object)
- returns an object with field constraints
field.descriptor
(Object)
- returns field descriptor
field.castValue(value, {constraints=true})
Cast given value according to the field type and format.
value (any)
- value to cast against fieldconstraints (Boolean/String[])
- gets constraints configuration- it could be set to true to disable constraint checks
- it could be an Array of constraints to check e.g. ['minimum', 'maximum']
(errors.TableSchemaError)
- raises any error occured in the process(any)
- returns cast value
field.testValue(value, {constraints=true})
Test if value is compliant to the field.
value (any)
- value to cast against fieldconstraints (Boolean/String[])
- constraints configuration(Boolean)
- returns if value is compliant to the field
Validate
validate()
validates whether a schema is a validate Table Schema accordingly to the specifications. It does not validate data against a schema.
Given a schema descriptor validate
returns Promise
with a validation object:
const {validate} = require('tableschema')
const {valid, errors} = await validate('schema.json')
for (const error of errors) {
// inspect Error objects
}
async validate(descriptor)
This funcion is async so it has to be used with await
keyword or as a Promise
.
descriptor (String/Object)
- schema descriptor (one of):- local path
- remote url
- object
(Object)
- returns{valid, errors}
object
Infer
Given data source and headers infer
will return a Table Schema as a JSON object based on the data values.
Given the data file, example.csv:
id,age,name
1,39,Paul
2,23,Jimmy
3,36,Jane
4,28,Judy
Call infer
with headers and values from the datafile:
const descriptor = await infer('data.csv')
The descriptor
variable is now a JSON object:
{
fields: [
{
name: 'id',
title: '',
description: '',
type: 'integer',
format: 'default'
},
{
name: 'age',
title: '',
description: '',
type: 'integer',
format: 'default'
},
{
name: 'name',
title: '',
description: '',
type: 'string',
format: 'default'
}
]
}
async infer(source, {headers=1, ...options})
This funcion is async so it has to be used with await
keyword or as a Promise
.
source (String/Array[]/Stream/Function)
- data source (one of):- local CSV file (path)
- remote CSV file (url)
- array of arrays representing the rows
- readable stream with CSV file contents
- function returning readable stream with CSV file contents
headers (String[])
- array of headersoptions (Object)
- anyTable.load
options(errors.TableSchemaError)
- raises any error occured in the process(Object)
- returns schema descriptor
Errors
errors.TableSchemaError
Base class for the all library errors. If there are more than one error you could get an additional information from the error object:
try {
// some lib action
} catch (error) {
console.log(error) // you have N cast errors (see error.errors)
if (error.multiple) {
for (const error of error.errors) {
console.log(error) // cast error M is ...
}
}
}
errors.tableSchemaError.rowNumber
(Number/undefined)
- row number of the error if available
errors.tableSchemaError.columnNumber
(Number/undefined)
- column number of the error if available
Contributing
The project follows the Open Knowledge International coding standards. There are common commands to work with the project:
$ npm install
$ npm run test
$ npm run build
Changelog
Here described only breaking and the most important changes. The full changelog and documentation for all released versions could be found in nicely formatted commit history.
v1.4
Improved behaviour:
- Now the
infer
functions support formats inferring
v1.3
New API added:
error.rowNumber
if availableerror.columnNumber
if available
v1.2
New API added:
Table.load
andinfer
now accept Node Stream as asource
argument
v1.1
New API added:
Table.load
andinfer
now acceptsparserOptions
v1.0
This version includes various big changes. A migration guide is under development and will be published here.
v0.2
First stable version of the library.