[GitHub] [arrow-datafusion] alamb commented on a change in pull request #1914: add metadata to DFSchema, close #1806.

[GitBox <gi...@apache.org>]

alamb commented on a change in pull request #1914:
URL: https://github.com/apache/arrow-datafusion/pull/1914#discussion_r820224374



##########
File path: datafusion-common/src/dfschema.rs
##########
@@ -36,16 +36,30 @@ pub type DFSchemaRef = Arc<DFSchema>;
 pub struct DFSchema {
     /// Fields
     fields: Vec<DFField>,
+    /// Additional metadata in form of key value pairs
+    metadata: HashMap<String, String>,
 }
 
 impl DFSchema {
     /// Creates an empty `DFSchema`
     pub fn empty() -> Self {
-        Self { fields: vec![] }
+        Self {
+            fields: vec![],
+            metadata: HashMap::new(),
+        }
     }
 
+    #[deprecated(since = "7.0.0", note = "please use `new_with_metadata` instead")]
     /// Create a new `DFSchema`
     pub fn new(fields: Vec<DFField>) -> Result<Self> {
+        Self::new_with_metadata(fields, HashMap::new())
+    }
+
+    /// Create a new `DFSchema`
+    pub fn new_with_metadata(

Review comment:
       What would you think about a more "builder-like" API here that perhaps could remain backwards compatible. 
   
   Something like:
   
   ```rust
   /// Sets the metadata on this DFSchema to `metadata`
   pub fn with_metadata(mut self, metadata: HashMap<String, String>) -> Self {
   ...
   }
   ```
   
   
   And then instead of code like
   
   ```rust
           Schema::new_with_metadata(
               df_schema.fields.iter().map(|f| f.field.clone()).collect(),
               df_schema.metadata.clone(),
           )
   ```
   
   It would look like
   ```rust
           Schema::new(
               df_schema.fields.iter().map(|f| f.field.clone()).collect(),
           )
           .with_metadata(df_schema.metadata.clone()),
   ```




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