sql.NullString || sql.NullInt64转换为普通格式json是否为null？ [关闭]

Question

Often happens in relational database, that when selecting records from the database, the field is returned. Go does not process strings and numbers as nil, in this case there is an auxiliary type of sql.Null {type} But if you return data in json format, then use of this type becomes unnecessary since, in javascript, there is null.

Now I sql.NullString convert to manual. Also there is a variant in sql itself to return, not null, and an empty line (if it is a line), but for some reasons in the future it will be difficult to debug.

How do you solve this problem?

Answer 1

Your question is a little confusing but I think I understand what you are asking. Inspired by another post that I can no longer find, I wrote wrappers around the sql.Null types to encode JSON as primitive types. See example below:

import (
    "database/sql"
    "encoding/json"
)

type JsonNullInt64 struct {
    sql.NullInt64
}

type JsonNullFloat64 struct {
    sql.NullFloat64
}

type JsonNullString struct {
    sql.NullString
}

type JsonNullBool struct {
    sql.NullBool
}

func (v *JsonNullBool) MarshalJSON() ([]byte, error) {
    if v.Valid {
        return json.Marshal(v.Bool)
    } else {
        return json.Marshal(nil)
    }
}

func (v *JsonNullBool) UnmarshalJSON(data []byte) error {
    var b *bool
    if err := json.Unmarshal(data, &b); err != nil {
        return err
    }

    if b != nil {
        v.Valid = true
        v.Bool = *b
    } else {
        v.Valid = false
    }

    return nil
}

func (v *JsonNullString) MarshalJSON() ([]byte, error) {
    if v.Valid {
        return json.Marshal(v.String)
    } else {
        return json.Marshal(nil)
    }
}

func (v *JsonNullString) UnmarshalJSON(data []byte) error {
    var str *string
    if err := json.Unmarshal(data, &str); err != nil {
        return err
    }

    if str != nil {
        v.Valid = true
        v.String = *str
    } else {
        v.Valid = false
    }

    return nil
}

func (v JsonNullFloat64) MarshalJSON() ([]byte, error) {
    if v.Valid {
        return json.Marshal(v.Float64)
    } else {
        return json.Marshal(0)
    }
}

func (v *JsonNullFloat64) UnmarshalJSON(data []byte) error {
    // Unmarshalling into a pointer will let us detect null

    var x *float64
    err := json.Unmarshal(data, &x)
    if err != nil {
        return err
    }
    if x != nil {
        v.Valid = true
        v.Float64 = *x
    } else {
        v.Valid = false
    }
    return nil
}

func (v JsonNullInt64) MarshalJSON() ([]byte, error) {
    if v.Valid {
        return json.Marshal(v.Int64)
    } else {
        return json.Marshal(0)
    }
}

func (v JsonNullInt64) UnmarshalJSON(data []byte) error {
    // Unmarshalling into a pointer will let us detect null
    var x *int64
    if err := json.Unmarshal(data, &x); err != nil {
        return err
    }
    if x != nil {
        v.Valid = true
        v.Int64 = *x
    } else {
        v.Valid = false
    }
    return nil
}