Migrating from go-playground/validator

This guide helps you migrate from go-playground/validator to Pedantigo.

---

Quick Migration (One Line)

For most codebases, migration requires only one line:

func init() {
    pedantigo.SetTagName("validate")
}

This tells Pedantigo to read your existing validate:"..." struct tags instead of pedantigo:"...".

Your existing structs work unchanged:

type User struct {
    Email string `json:"email" validate:"required,email"`
    Age   int    `json:"age" validate:"min=18,max=120"`
}

// Works with Pedantigo
user, err := pedantigo.Unmarshal[User](jsonData)

---

Supported Tags (Zero Changes Needed)

These validator tags work identically in Pedantigo:

Core Constraints

required, min, max, len, eq, ne, gt, gte, lt, lte

String Constraints

email, url, uri, uuid, alpha, alphanum, alphaunicode, alphanumunicode, numeric, number, hexadecimal, ascii, printascii, lowercase, uppercase, contains, excludes, startswith, endswith, startsnotwith, endsnotwith, containsany, excludesall, excludesrune

Enum/Choice

oneof, oneofci

Field Comparisons

eqfield, nefield, gtfield, gtefield, ltfield, ltefield, eqcsfield, necsfield, gtcsfield, gtecsfield, ltcsfield, ltecsfield

Conditional Validation

required_if, required_unless, required_with, required_without, required_with_all, required_without_all, excluded_if, excluded_unless, excluded_with, excluded_without, excluded_with_all, excluded_without_all

Network

ip, ipv4, ipv6, cidr, cidrv4, cidrv6, mac, hostname, hostname_rfc1123, fqdn, tcp_addr, udp_addr, hostname_port, http_url

Format Validators

datetime, credit_card, isbn, isbn10, isbn13, issn, ssn, ein, e164, base64, base64url, base64rawurl, json, jwt, html, hexcolor, rgb, rgba, hsl, hsla, latitude, longitude, md4, md5, sha256, sha384, sha512, mongodb, cron, semver, ulid, luhn_checksum, bitcoin_addr, bitcoin_addr_bech32, ethereum_addr

ISO Codes

iso3166_1_alpha2, iso3166_1_alpha3, iso3166_1_alpha_numeric, iso4217, bcp47_language_tag, postcode_iso3166_alpha2

Collections

dive, unique

OR Operator

hexcolor|rgb|rgba (validates if ANY matches)

Aliases

iscolor (expands to hexcolor|rgb|rgba|hsl|hsla)

---

Tags You Can Remove

These validator tags are not needed in Pedantigo:

Tag	Why Not Needed
omitempty	Pedantigo tracks JSON field presence. Empty values skip validation unless required.
omitnil	Nil pointers are handled automatically.
omitzero	Zero values skip validation unless required.
-	Simply don't add a tag.
structonly	Not needed - Pedantigo validates all fields by default.
nostructlevel	Not needed.
isdefault	Not needed - check for zero value in code.

Example migration:

// validator
Email string `validate:"omitempty,email"`

// pedantigo (same behavior)
Email string `validate:"email"`

---

Custom Validator Registration

RegisterAlias

// validator
validate.RegisterAlias("is_active", "oneof=active enabled")

// pedantigo (identical)
pedantigo.RegisterAlias("is_active", "oneof=active enabled")

Custom Validators

// validator
validate.RegisterValidation("custom", customFunc)

// pedantigo
pedantigo.RegisterConstraint("custom", func(value string) (constraints.Constraint, bool) {
    return &myCustomConstraint{}, true
})

---

Features NOT Supported

The following validator features are not available in Pedantigo:

Feature	validator Syntax	Workaround
Var()	v.Var(email, "email")	Use struct with single field
StructPartial	Validate subset of fields	Not supported
StructExcept	Exclude fields from validation	Not supported
RegisterValidationCtx	Context-aware validation	Pass context as struct field
RegisterTagNameFunc	Custom field name function	Uses JSON tag by default
skip_unless	Skip unless condition	Implement in struct-level validator
eq_ignore_case	Case-insensitive equality	Use to_lower,eq=value
ne_ignore_case	Case-insensitive not-equal	Use to_lower,ne=value
containsrune	Contains specific rune	Use containsany=X with single char
https_url	URL with https:// only	Use http_url or url,startswith=https://
multibyte	Has multibyte characters	Use regexp
datauri	Data URI format	Use regexp
base32	Base32 encoding	Use regexp
urn_rfc2141	URN format	Use regexp
uuid3/4/5	Specific UUID version	uuid accepts all versions
timezone	IANA timezone	Custom validator
image	File is image	Filesystem check in code

For a complete feature comparison, see API Parity.

These features might be added in the future. If you need any of these features, please open a GitHub issue with your use case.

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What You Gain

Pedantigo provides features not available in validator:

Feature	Description
JSON Schema generation	pedantigo.Schema[User]()
Unmarshal + Validate	Single step: pedantigo.Unmarshal[User](json)
Streaming validation	Parse partial JSON for LLM output
Discriminated unions	Union[TypeA, TypeB, TypeC]
ExtraAllow mode	Capture unknown JSON fields
Secret types	Secret[string] masks in logs
Transformers	strip_whitespace, to_lower, to_upper
Default values	default=value

---

Step-by-Step Migration

1. Add the tag override:

   func init() {
       pedantigo.SetTagName("validate")
   }

2. Replace validation calls:

   // Before (validator)
   validate := validator.New()
   err := validate.Struct(user)
   
   // After (pedantigo)
   user, err := pedantigo.Unmarshal[User](jsonData)
   // or
   err := pedantigo.Validate(&user)

3. Remove unnecessary tags:

   • Delete omitempty, omitnil, omitzero
   • Delete - tags (just remove the tag entirely)

4. Test your structs:

   go test ./...

5. Optional: Migrate tag name: Once validated, you can gradually rename validate to pedantigo tags if desired.

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Troubleshooting

"unknown constraint" error

Check if the constraint is in the unsupported list. Use the suggested workaround or implement a custom validator.

Different validation behavior

Pedantigo may have stricter or different validation for some formats. Test edge cases and adjust if needed.

Missing Var() function

Wrap the value in a struct:

// validator
err := validate.Var(email, "required,email")

// pedantigo
type EmailWrapper struct {
    Email string `validate:"required,email"`
}
_, err := pedantigo.Unmarshal[EmailWrapper]([]byte(`{"Email":"` + email + `"}`))