diff --git a/src/schema.rs b/src/schema.rs
index 6e9c6af..b64e769 100644
--- a/src/schema.rs
+++ b/src/schema.rs
@@ -1,3 +1,5 @@
+use std::str::FromStr;
+
 use crate::*;
 use indexmap::IndexMap;
 use serde::{Deserialize, Serialize};
@@ -228,6 +230,18 @@ pub enum NumberFormat {
     Double,
 }
 
+impl FromStr for NumberFormat {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "float" => Ok(Self::Float),
+            "double" => Ok(Self::Double),
+            _ => Err(()),
+        }
+    }
+}
+
 #[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq)]
 #[serde(rename_all = "lowercase")]
 pub enum IntegerFormat {
@@ -235,17 +249,43 @@ pub enum IntegerFormat {
     Int64,
 }
 
+impl FromStr for IntegerFormat {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "int32" => Ok(Self::Int32),
+            "int64" => Ok(Self::Int64),
+            _ => Err(()),
+        }
+    }
+}
+
 #[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq)]
 #[serde(rename_all = "lowercase")]
 pub enum StringFormat {
     Date,
-    #[serde(rename = "date-time")]
     DateTime,
     Password,
     Byte,
     Binary,
 }
 
+impl FromStr for StringFormat {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "date" => Ok(Self::Date),
+            "date-time" => Ok(Self::DateTime),
+            "password" => Ok(Self::Password),
+            "byte" => Ok(Self::Byte),
+            "binary" => Ok(Self::Binary),
+            _ => Err(()),
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use serde_json::json;
diff --git a/src/variant_or.rs b/src/variant_or.rs
index 9b2fdbc..a7f80dd 100644
--- a/src/variant_or.rs
+++ b/src/variant_or.rs
@@ -1,3 +1,5 @@
+use std::str::FromStr;
+
 use serde::{Deserialize, Serialize};
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
@@ -7,6 +9,18 @@ pub enum VariantOrUnknown<T> {
     Unknown(String),
 }
 
+impl<T> From<String> for VariantOrUnknown<T>
+where
+    T: FromStr,
+{
+    fn from(s: String) -> Self {
+        match T::from_str(&s) {
+            Ok(t) => Self::Item(t),
+            Err(_) => Self::Unknown(s),
+        }
+    }
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
 #[serde(untagged)]
 pub enum VariantOrUnknownOrEmpty<T> {
@@ -29,3 +43,39 @@ impl<T> Default for VariantOrUnknownOrEmpty<T> {
         VariantOrUnknownOrEmpty::Empty
     }
 }
+
+impl<T> From<Option<String>> for VariantOrUnknownOrEmpty<T>
+where
+    T: FromStr,
+{
+    fn from(v: Option<String>) -> Self {
+        match v {
+            Some(s) => match T::from_str(&s) {
+                Ok(t) => VariantOrUnknownOrEmpty::Item(t),
+                Err(_) => VariantOrUnknownOrEmpty::Unknown(s),
+            },
+            None => VariantOrUnknownOrEmpty::Empty,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{StringFormat, VariantOrUnknownOrEmpty};
+
+    #[test]
+    fn test_variant_from() {
+        assert_eq!(
+            VariantOrUnknownOrEmpty::<StringFormat>::from(None),
+            VariantOrUnknownOrEmpty::Empty,
+        );
+        assert_eq!(
+            VariantOrUnknownOrEmpty::<StringFormat>::from(Some("date".to_string())),
+            VariantOrUnknownOrEmpty::Item(StringFormat::Date),
+        );
+        assert_eq!(
+            VariantOrUnknownOrEmpty::<StringFormat>::from(Some("yolo".to_string())),
+            VariantOrUnknownOrEmpty::Unknown("yolo".to_string()),
+        );
+    }
+}