Add "checked" variant of set_category()

libimagentrycategory/src/category.rs

@@ -28,6 +28,7 @@ use libimagerror::into::IntoError;
 use error::CategoryErrorKind as CEK;
 use error::MapErrInto;
 use result::Result;
+use register::CategoryRegister;
 
 #[derive(Clone, Debug, Eq, PartialEq, Ord, PartialOrd)]
 pub struct Category(String);
@@ -49,6 +50,9 @@ impl Into<String> for Category {
 pub trait EntryCategory {
 
     fn set_category(&mut self, s: Category) -> Result<()>;
+
+    fn set_category_checked(&mut self, register: &CategoryRegister, s: Category) -> Result<()>;
+
     fn get_category(&self) -> Result<Option<Category>>;
 
     fn has_category(&self) -> Result<bool>;
@@ -64,6 +68,18 @@ impl EntryCategory for Entry {
             .map(|_| ())
     }
 
+    /// Check whether a category exists before setting it.
+    ///
+    /// This function should be used by default over EntryCategory::set_category()!
+    fn set_category_checked(&mut self, register: &CategoryRegister, s: Category) -> Result<()> {
+        register.category_exists(&s.0)
+            .and_then(|bl| if bl {
+                self.set_category(s)
+            } else {
+                Err(CEK::CategoryDoesNotExist.into_error())
+            })
+    }
+
     fn get_category(&self) -> Result<Option<Category>> {
         match self.get_header().read(&String::from("category.value")) {
             Err(res) => match res.kind() {

libimagentrycategory/src/error.rs

@@ -24,7 +24,9 @@ generate_error_module!(
         StoreIdHandlingError => "StoreId handling error",
         HeaderReadError  => "Header read error",
         HeaderWriteError => "Header write error",
-        TypeError        => "Found wrong type in header"
+        TypeError        => "Found wrong type in header",
+
+        CategoryDoesNotExist => "Category does not exist"
     );
 );