gotosocial/vendor/go.mongodb.org/mongo-driver/bson/doc.go

140 lines
7.9 KiB
Go

// Copyright (C) MongoDB, Inc. 2017-present.
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may
// not use this file except in compliance with the License. You may obtain
// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
// Package bson is a library for reading, writing, and manipulating BSON. BSON is a binary serialization format used to
// store documents and make remote procedure calls in MongoDB. The BSON specification is located at https://bsonspec.org.
// The BSON library handles marshaling and unmarshaling of values through a configurable codec system. For a description
// of the codec system and examples of registering custom codecs, see the bsoncodec package. For additional information
// and usage examples, check out the [Work with BSON] page in the Go Driver docs site.
//
// # Raw BSON
//
// The Raw family of types is used to validate and retrieve elements from a slice of bytes. This
// type is most useful when you want do lookups on BSON bytes without unmarshaling it into another
// type.
//
// Example:
//
// var raw bson.Raw = ... // bytes from somewhere
// err := raw.Validate()
// if err != nil { return err }
// val := raw.Lookup("foo")
// i32, ok := val.Int32OK()
// // do something with i32...
//
// # Native Go Types
//
// The D and M types defined in this package can be used to build representations of BSON using native Go types. D is a
// slice and M is a map. For more information about the use cases for these types, see the documentation on the type
// definitions.
//
// Note that a D should not be constructed with duplicate key names, as that can cause undefined server behavior.
//
// Example:
//
// bson.D{{"foo", "bar"}, {"hello", "world"}, {"pi", 3.14159}}
// bson.M{"foo": "bar", "hello": "world", "pi": 3.14159}
//
// When decoding BSON to a D or M, the following type mappings apply when unmarshaling:
//
// 1. BSON int32 unmarshals to an int32.
// 2. BSON int64 unmarshals to an int64.
// 3. BSON double unmarshals to a float64.
// 4. BSON string unmarshals to a string.
// 5. BSON boolean unmarshals to a bool.
// 6. BSON embedded document unmarshals to the parent type (i.e. D for a D, M for an M).
// 7. BSON array unmarshals to a bson.A.
// 8. BSON ObjectId unmarshals to a primitive.ObjectID.
// 9. BSON datetime unmarshals to a primitive.DateTime.
// 10. BSON binary unmarshals to a primitive.Binary.
// 11. BSON regular expression unmarshals to a primitive.Regex.
// 12. BSON JavaScript unmarshals to a primitive.JavaScript.
// 13. BSON code with scope unmarshals to a primitive.CodeWithScope.
// 14. BSON timestamp unmarshals to an primitive.Timestamp.
// 15. BSON 128-bit decimal unmarshals to an primitive.Decimal128.
// 16. BSON min key unmarshals to an primitive.MinKey.
// 17. BSON max key unmarshals to an primitive.MaxKey.
// 18. BSON undefined unmarshals to a primitive.Undefined.
// 19. BSON null unmarshals to nil.
// 20. BSON DBPointer unmarshals to a primitive.DBPointer.
// 21. BSON symbol unmarshals to a primitive.Symbol.
//
// The above mappings also apply when marshaling a D or M to BSON. Some other useful marshaling mappings are:
//
// 1. time.Time marshals to a BSON datetime.
// 2. int8, int16, and int32 marshal to a BSON int32.
// 3. int marshals to a BSON int32 if the value is between math.MinInt32 and math.MaxInt32, inclusive, and a BSON int64
// otherwise.
// 4. int64 marshals to BSON int64 (unless [Encoder.IntMinSize] is set).
// 5. uint8 and uint16 marshal to a BSON int32.
// 6. uint, uint32, and uint64 marshal to a BSON int64 (unless [Encoder.IntMinSize] is set).
// 7. BSON null and undefined values will unmarshal into the zero value of a field (e.g. unmarshaling a BSON null or
// undefined value into a string will yield the empty string.).
//
// # Structs
//
// Structs can be marshaled/unmarshaled to/from BSON or Extended JSON. When transforming structs to/from BSON or Extended
// JSON, the following rules apply:
//
// 1. Only exported fields in structs will be marshaled or unmarshaled.
//
// 2. When marshaling a struct, each field will be lowercased to generate the key for the corresponding BSON element.
// For example, a struct field named "Foo" will generate key "foo". This can be overridden via a struct tag (e.g.
// `bson:"fooField"` to generate key "fooField" instead).
//
// 3. An embedded struct field is marshaled as a subdocument. The key will be the lowercased name of the field's type.
//
// 4. A pointer field is marshaled as the underlying type if the pointer is non-nil. If the pointer is nil, it is
// marshaled as a BSON null value.
//
// 5. When unmarshaling, a field of type interface{} will follow the D/M type mappings listed above. BSON documents
// unmarshaled into an interface{} field will be unmarshaled as a D.
//
// The encoding of each struct field can be customized by the "bson" struct tag.
//
// This tag behavior is configurable, and different struct tag behavior can be configured by initializing a new
// bsoncodec.StructCodec with the desired tag parser and registering that StructCodec onto the Registry. By default, JSON
// tags are not honored, but that can be enabled by creating a StructCodec with JSONFallbackStructTagParser, like below:
//
// Example:
//
// structcodec, _ := bsoncodec.NewStructCodec(bsoncodec.JSONFallbackStructTagParser)
//
// The bson tag gives the name of the field, possibly followed by a comma-separated list of options.
// The name may be empty in order to specify options without overriding the default field name. The following options can
// be used to configure behavior:
//
// 1. omitempty: If the omitempty struct tag is specified on a field, the field will be omitted from the marshaling if
// the field has an empty value, defined as false, 0, a nil pointer, a nil interface value, and any empty array,
// slice, map, or string.
// NOTE: It is recommended that this tag be used for all slice and map fields.
//
// 2. minsize: If the minsize struct tag is specified on a field of type int64, uint, uint32, or uint64 and the value of
// the field can fit in a signed int32, the field will be serialized as a BSON int32 rather than a BSON int64. For
// other types, this tag is ignored.
//
// 3. truncate: If the truncate struct tag is specified on a field with a non-float numeric type, BSON doubles
// unmarshaled into that field will be truncated at the decimal point. For example, if 3.14 is unmarshaled into a
// field of type int, it will be unmarshaled as 3. If this tag is not specified, the decoder will throw an error if
// the value cannot be decoded without losing precision. For float64 or non-numeric types, this tag is ignored.
//
// 4. inline: If the inline struct tag is specified for a struct or map field, the field will be "flattened" when
// marshaling and "un-flattened" when unmarshaling. This means that all of the fields in that struct/map will be
// pulled up one level and will become top-level fields rather than being fields in a nested document. For example,
// if a map field named "Map" with value map[string]interface{}{"foo": "bar"} is inlined, the resulting document will
// be {"foo": "bar"} instead of {"map": {"foo": "bar"}}. There can only be one inlined map field in a struct. If
// there are duplicated fields in the resulting document when an inlined struct is marshaled, the inlined field will
// be overwritten. If there are duplicated fields in the resulting document when an inlined map is marshaled, an
// error will be returned. This tag can be used with fields that are pointers to structs. If an inlined pointer field
// is nil, it will not be marshaled. For fields that are not maps or structs, this tag is ignored.
//
// # Marshaling and Unmarshaling
//
// Manually marshaling and unmarshaling can be done with the Marshal and Unmarshal family of functions.
//
// [Work with BSON]: https://www.mongodb.com/docs/drivers/go/current/fundamentals/bson/
package bson