schema

Documentation

Index

• Constants
• type Field
  • func (f *Field) Decode(value string) (interface{}, error)
  • func (f *Field) Encode(in interface{}) (string, error)
  • func (f *Field) TestString(value string) bool
  • func (f *Field) UnmarshalJSON(data []byte) error
• type Fields
  • func (f Fields) Len() int
  • func (f Fields) Less(i, j int) bool
  • func (f Fields) Swap(i, j int)
• type ForeignKeyReference
• type ForeignKeys
• type GeoPoint
  • func (p *GeoPoint) UnmarshalJSON(data []byte) error
• type Schema
  • func Infer(tab table.Table) (*Schema, error)
  • func InferImplicitCasting(tab table.Table) (*Schema, error)
  • func LoadFromFile(path string) (*Schema, error)
  • func LoadRemote(url string) (*Schema, error)
  • func Read(r io.Reader) (*Schema, error)
  • func (s *Schema) Decode(row []string, out interface{}) error
  • func (s *Schema) DecodeTable(tab table.Table, out interface{}) error
  • func (s *Schema) Encode(in interface{}) ([]string, error)
  • func (s *Schema) EncodeTable(in interface{}) ([][]string, error)
  • func (s *Schema) GetField(name string) (*Field, int)
  • func (s *Schema) HasField(name string) bool
  • func (s *Schema) MarshalJSON() ([]byte, error)
  • func (s *Schema) SaveToFile(path string) error
  • func (s *Schema) UnmarshalJSON(data []byte) error
  • func (s *Schema) Validate() error
  • func (s *Schema) Write(w io.Writer) error

Examples

• InferImplicitCasting
• Schema.Decode
• Schema.DecodeTable
• Schema.Encode
• Schema.EncodeTable

Constants

const (
	IntegerType   = "integer"
	StringType    = "string"
	BooleanType   = "boolean"
	NumberType    = "number"
	DateType      = "date"
	ObjectType    = "object"
	ArrayType     = "array"
	DateTimeType  = "datetime"
	TimeType      = "time"
	YearMonthType = "yearmonth"
	YearType      = "year"
	DurationType  = "duration"
	GeoPointType  = "geopoint"
	AnyType       = "any"
)

Field types.

const (
	GeoPointArrayFormat  = "array"
	GeoPointObjectFormat = "object"
)

Formats specific to GeoPoint field type.

const (
	AnyDateFormat = "any"
)

Formats.

const InvalidPosition = -1

InvalidPosition is returned by GetField call when it refers to a field that does not exist in the schema.

Types

type Field

type Field struct {
	// Name of the field. It is mandatory and shuold correspond to the name of field/column in the data file (if it has a name).
	Name   string `json:"name"`
	Type   string `json:"type,omitempty"`
	Format string `json:"format,omitempty"`
	// A human readable label or title for the field.
	Title string `json:"title,omitempty"`
	// A description for this field e.g. "The recipient of the funds"
	Description string `json:"description,omitempty"`

	// Boolean properties. Define set of the values that represent true and false, respectively.
	// https://specs.frictionlessdata.io/table-schema/#boolean
	TrueValues  []string `json:"trueValues,omitempty"`
	FalseValues []string `json:"falseValues,omitempty"`

	// A string whose value is used to represent a decimal point within the number. The default value is ".".
	DecimalChar string `json:"decimalChar,omitempty"`
	// A string whose value is used to group digits within the number. The default value is null. A common value is "," e.g. "100,000".
	GroupChar string `json:"groupChar,omitempty"`
	// If true the physical contents of this field must follow the formatting constraints already set out.
	// If false the contents of this field may contain leading and/or trailing non-numeric characters which
	// are going to be stripped. Default value is true:
	BareNumber bool `json:"bareNumber,omitempty"`
}

Field describes a single field in the table schema. More: https://specs.frictionlessdata.io/table-schema/#field-descriptors

func (*Field) Decode

func (f *Field) Decode(value string) (interface{}, error)

Decode decodes the passed-in string against field type. Returns an error if the value can not be cast or any field constraint can not be satisfied.

func (*Field) Encode

func (f *Field) Encode(in interface{}) (string, error)

Encode encodes the passed-in value into a string. It returns an error if the the type of the passed-in value can not be converted to field type.

func (*Field) TestString

func (f *Field) TestString(value string) bool

TestString checks whether the value can be unmarshalled to the field type.

func (*Field) UnmarshalJSON

func (f *Field) UnmarshalJSON(data []byte) error

UnmarshalJSON sets *f to a copy of data. It will respect the default values described at: https://specs.frictionlessdata.io/table-schema/

type Fields

type Fields []Field

Fields represents a list of schema fields.

func (Fields) Len

func (f Fields) Len() int

func (Fields) Less

func (f Fields) Less(i, j int) bool

func (Fields) Swap

func (f Fields) Swap(i, j int)

type ForeignKeyReference

type ForeignKeyReference struct {
	Resource          string      `json:"resource,omitempty"`
	Fields            []string    `json:"-"`
	FieldsPlaceholder interface{} `json:"fields,omitempty"`
}

ForeignKeyReference represents the field reference by a foreign key.

type ForeignKeys

type ForeignKeys struct {
	Fields            []string            `json:"-"`
	FieldsPlaceholder interface{}         `json:"fields,omitempty"`
	Reference         ForeignKeyReference `json:"reference,omitempty"`
}

ForeignKeys defines a schema foreign key

type GeoPoint

type GeoPoint struct {
	Lon float64 `json:"lon,omitempty"`
	Lat float64 `json:"lat,omitempty"`
}

GeoPoint represents a "geopoint" cell. More at: https://specs.frictionlessdata.io/table-schema/#geopoint

func (*GeoPoint) UnmarshalJSON

func (p *GeoPoint) UnmarshalJSON(data []byte) error

UnmarshalJSON sets *f to a copy of data. It will respect the default values

type Schema

type Schema struct {
	Fields                Fields      `json:"fields,omitempty"`
	PrimaryKeyPlaceholder interface{} `json:"primaryKey,omitempty"`
	PrimaryKeys           []string    `json:"-"`
	ForeignKeys           ForeignKeys `json:"foreignKeys,omitempty"`
	MissingValues         []string    `json:"missingValues,omitempty"`
}

Schema describes tabular data.

func Infer

func Infer(tab table.Table) (*Schema, error)

Infer infers a schema from a slice of the tabular data. For columns that contain cells that can inferred as different types, the most popular type is set as the field type. For instance, a column with values 10.1, 10, 10 will inferred as being of type "integer".

func InferImplicitCasting

func InferImplicitCasting(tab table.Table) (*Schema, error)

InferImplicitCasting uses a implicit casting for infering the type of columns that have cells of diference types. For instance, a column with values 10.1, 10, 10 will inferred as being of type "number" ("integer" can be implicitly cast to "number").

For medium to big tables, this method is faster than the Infer.

Example

tab := table.FromSlices(
	[]string{"Person", "Height"},
	[][]string{
		[]string{"Foo", "5"},
		[]string{"Bar", "4"},
		[]string{"Bez", "5.5"},
	})
s, _ := InferImplicitCasting(tab)
fmt.Println("Fields:")
for _, f := range s.Fields {
	fmt.Printf("{Name:%s Type:%s Format:%s}\n", f.Name, f.Type, f.Format)
}

Output:

Fields:
{Name:Person Type:string Format:default}
{Name:Height Type:number Format:default}

func LoadFromFile

func LoadFromFile(path string) (*Schema, error)

LoadFromFile loads and parses a schema descriptor from a local file.

func LoadRemote

func LoadRemote(url string) (*Schema, error)

LoadRemote downloads and parses a schema descriptor from the specified URL.

func Read

func Read(r io.Reader) (*Schema, error)

Read reads and parses a descriptor to create a schema.

Example - Reading a schema from a file:

f, err := os.Open("foo/bar/schema.json")
if err != nil {
  panic(err)
}
s, err := Read(f)
if err != nil {
  panic(err)
}
fmt.Println(s)

func (*Schema) Decode

func (s *Schema) Decode(row []string, out interface{}) error

Decode decodes the passed-in row to schema types and stores it in the value pointed by out. The out value must be pointer to a struct. Only exported fields will be unmarshalled. The lowercased field name is used as the key for each exported field.

If a value in the row cannot be marshalled to its respective schema field (Field.Unmarshal), this call will return an error. Furthermore, this call is also going to return an error if the schema field value can not be unmarshalled to the struct field type.

Example

// Lets assume we have a schema ...
s := Schema{Fields: []Field{{Name: "Name", Type: StringType}, {Name: "Age", Type: IntegerType}}}

// And a Table.
t := table.FromSlices([]string{"Name", "Age"}, [][]string{
	{"Foo", "42"},
	{"Bar", "43"}})

// And we would like to process them using Go types. First we need to create a struct to hold the
// content of each row.
type person struct {
	Name string
	Age  int
}

// Now it is a matter of iterate over the table and Decode each row.
iter, _ := t.Iter()
for iter.Next() {
	var p person
	s.Decode(iter.Row(), &p)
	fmt.Printf("%+v\n", p)
}

Output:

{Name:Foo Age:42}
{Name:Bar Age:43}

func (*Schema) DecodeTable

func (s *Schema) DecodeTable(tab table.Table, out interface{}) error

DecodeTable loads and decodes all table rows.

The result argument must necessarily be the address for a slice. The slice may be nil or previously allocated.

Example

// Lets assume we have a schema ...
s := Schema{Fields: []Field{{Name: "Name", Type: StringType}, {Name: "Age", Type: IntegerType}}}

// And a Table.
t := table.FromSlices([]string{"Name", "Age"}, [][]string{
	{"Foo", "42"},
	{"Bar", "43"}})

// And we would like to process them using Go types. First we need to create a struct to hold the
// content of each row.
type person struct {
	Name string
	Age  int
}
var people []person
s.DecodeTable(t, &people)
fmt.Print(people)

Output:

[{Foo 42} {Bar 43}]

func (*Schema) Encode

func (s *Schema) Encode(in interface{}) ([]string, error)

Encode encodes struct into a row. This method can only encode structs (or pointer to structs) and will error out if nil is passed.

Example

// Lets assume we have a schema.
s := Schema{Fields: []Field{{Name: "Name", Type: StringType}, {Name: "Age", Type: IntegerType}}}

// And would like to create a CSV out of this list conforming to
// to the schema above.
people := []struct {
	Name string
	Age  int
}{{"Foo", 42}, {"Bar", 43}}

// First create the writer and write the header.
w := table.NewStringWriter()
w.Write([]string{"Name", "Age"})

// Then write the list
for _, person := range people {
	row, _ := s.Encode(person)
	w.Write(row)
}
w.Flush()
fmt.Print(w.String())

Output:

Name,Age
Foo,42
Bar,43

func (*Schema) EncodeTable

func (s *Schema) EncodeTable(in interface{}) ([][]string, error)

EncodeTable encodes each element (struct) of the passed-in slice and

Example

// Lets assume we have a schema.
s := Schema{Fields: []Field{{Name: "Name", Type: StringType}, {Name: "Age", Type: IntegerType}}}

// And would like to create a CSV out of this list conforming to
// to the schema above.
people := []struct {
	Name string
	Age  int
}{{"Foo", 42}, {"Bar", 43}}

// Then encode the people slice into a slice of rows.
rows, _ := s.EncodeTable(people)

// Now, simply write it down.
w := table.NewStringWriter()
w.Write([]string{"Name", "Age"})
w.WriteAll(rows)
w.Flush()
fmt.Print(w.String())

Output:

Name,Age
Foo,42
Bar,43

func (*Schema) GetField

func (s *Schema) GetField(name string) (*Field, int)

GetField fetches the index and field referenced by the name argument.

func (*Schema) HasField

func (s *Schema) HasField(name string) bool

HasField returns checks whether the schema has a field with the passed-in.

func (*Schema) MarshalJSON

func (s *Schema) MarshalJSON() ([]byte, error)

MarshalJSON returns the JSON encoding of s.

func (*Schema) SaveToFile

func (s *Schema) SaveToFile(path string) error

SaveToFile writes the schema descriptor in local file.

func (*Schema) UnmarshalJSON

func (s *Schema) UnmarshalJSON(data []byte) error

UnmarshalJSON sets *f to a copy of data. It will respect the default values described at: https://specs.frictionlessdata.io/table-schema/

func (*Schema) Validate

func (s *Schema) Validate() error

Validate checks whether the schema is valid. If it is not, returns an error describing the problem. More at: https://specs.frictionlessdata.io/table-schema/

func (*Schema) Write

func (s *Schema) Write(w io.Writer) error

Write writes the schema descriptor.