Struct ValidationError 

pub struct ValidationError {
    pub error_type: &'static str,
    pub loc: Vec<LocItem>,
    pub msg: String,
    pub input: Option<Value>,
    pub ctx: Option<HashMap<String, Value>>,
}

A single validation error item.

This structure matches FastAPI/Pydantic v2’s validation error format exactly, allowing for seamless compatibility with clients expecting FastAPI responses.

Examples

use fastapi_core::error::{ValidationError, loc, error_types};
use serde_json::json;

// Missing required field
let error = ValidationError::missing(loc::query("q"));
assert_eq!(error.error_type, "missing");

// String too short with context
let error = ValidationError::new(error_types::STRING_TOO_SHORT, loc::body_field("name"))
    .with_msg("String should have at least 3 characters")
    .with_input(json!("ab"))
    .with_ctx_value("min_length", json!(3));

Fields

error_type: &'static str

Error type identifier (e.g., “missing”, “string_too_short”).

loc: Vec<LocItem>

Location path as a tuple of strings and integers.

Examples:

• ["query", "q"] for query parameter
• ["body", "user", "email"] for nested body field
• ["body", "items", 0, "name"] for array item

msg: String

Human-readable error message.

input: Option<Value>

The input value that failed validation.

This is the actual value the user provided that caused the error.

ctx: Option<HashMap<String, Value>>

Additional context about the validation constraint.

Examples:

• {"min_length": 3} for string_too_short
• {"ge": 0} for greater_than_equal
• {"pattern": "^\\d+$"} for pattern mismatch

Implementations

impl ValidationError

pub fn new(error_type: &'static str, loc: Vec<LocItem>) -> ValidationError

Create a new validation error.

pub fn missing(loc: Vec<LocItem>) -> ValidationError

Create a “missing” error for a required field.

pub fn string_too_short(loc: Vec<LocItem>, min_length: usize) -> ValidationError

Create a “string_too_short” error.

pub fn string_too_long(loc: Vec<LocItem>, max_length: usize) -> ValidationError

Create a “string_too_long” error.

pub fn type_error( loc: Vec<LocItem>, expected_type: &'static str, ) -> ValidationError

Create a type error (e.g., expected int, got string).

pub fn json_invalid( loc: Vec<LocItem>, message: impl Into<String>, ) -> ValidationError

Create a JSON parsing error.

pub fn with_msg(self, msg: impl Into<String>) -> ValidationError

Set the human-readable message.

pub fn with_input(self, input: Value) -> ValidationError

Set the input value.

pub fn with_ctx_value( self, key: impl Into<String>, value: Value, ) -> ValidationError

Add a context key-value pair.

pub fn with_ctx(self, ctx: HashMap<String, Value>) -> ValidationError

Set the full context map.

pub fn with_loc_prefix(self, prefix: Vec<LocItem>) -> ValidationError

Add location items to the path.

pub fn with_loc_suffix(self, item: impl Into<LocItem>) -> ValidationError

Append a location item to the path.

pub fn greater_than_equal<T>(loc: Vec<LocItem>, min: T) -> ValidationError

where T: Display,

Create a “greater_than_equal” error for minimum value constraint.

pub fn less_than_equal<T>(loc: Vec<LocItem>, max: T) -> ValidationError

where T: Display,

Create a “less_than_equal” error for maximum value constraint.

pub fn pattern_mismatch(loc: Vec<LocItem>, pattern: &str) -> ValidationError

Create a “string_pattern_mismatch” error for regex pattern constraint.

pub fn invalid_email(loc: Vec<LocItem>) -> ValidationError

Create a “value_error” for invalid email format.

pub fn invalid_url(loc: Vec<LocItem>) -> ValidationError

Create a “value_error” for invalid URL format.

pub fn invalid_uuid(loc: Vec<LocItem>) -> ValidationError

Create a “value_error” for invalid UUID format.

pub fn value_error(loc: Vec<LocItem>, msg: impl Into<String>) -> ValidationError

Create a generic “value_error” with custom message.

Trait Implementations

impl Clone for ValidationError

fn clone(&self) -> ValidationError

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ValidationError

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Extend<ValidationError> for ValidationErrors

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = ValidationError>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl FromIterator<ValidationError> for ValidationErrors

fn from_iter<T>(iter: T) -> ValidationErrors

where T: IntoIterator<Item = ValidationError>,

Creates a value from an iterator.

impl Serialize for ValidationError

fn serialize<__S>( &self, __serializer: __S, ) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.