add validation doc

docs/content/docs/adding-crud-models.md

@@ -23,6 +23,8 @@ pub struct Model {
     pub id: i32,
     pub comment: String
 }
+
+impl ActixAdminModelValidationTrait<ActiveModel> for Entity {}
 ```
 
 ## Derive Implementations

docs/content/docs/validation.md

@@ -0,0 +1,35 @@
+---
+title: "Validation"
+date: 2023-01-17T11:44:56+01:00
+draft: false
+weight: 5
+---
+
+# Validation
+
+Models can be validated before writing to the database. In order to validate, the ValidationTrait needs to be implemented as in the following example.
+
+```rust
+#[derive(Clone, Debug, PartialEq, DeriveEntityModel, Deserialize, Serialize, DeriveActixAdmin, DeriveActixAdminModel, DeriveActixAdminViewModel)]
+#[sea_orm(table_name = "comment")]
+pub struct Model {
+    #[sea_orm(primary_key)]
+    #[serde(skip_deserializing)]
+    #[actix_admin(primary_key)]
+    pub id: i32,
+
+    pub my_decimal: Decimal
+}
+
+impl ActixAdminModelValidationTrait<ActiveModel> for Entity {
+    fn validate(model: &ActiveModel) -> HashMap<String, String> {
+        let mut errors = HashMap::new();
+        
+        if model.my_decimal.clone().unwrap() < Decimal::from(100 as i16) {
+            errors.insert("my_decimal".to_string(), "Must be larger than 100".to_string());
+        }
+
+        errors
+    }
+}
+```

examples/basic/entity/comment.rs

@@ -46,6 +46,7 @@ impl ActixAdminModelValidationTrait<ActiveModel> for Entity {
         if model.my_decimal.clone().unwrap() < Decimal::from(100 as i16) {
             errors.insert("my_decimal".to_string(), "Must be larger than 100".to_string());
         }
+
         errors
     }
 }