[arrow-datafusion] branch master updated: Improve error message and comments (#641)

[al...@apache.org]

This is an automated email from the ASF dual-hosted git repository.

alamb pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/arrow-datafusion.git


The following commit(s) were added to refs/heads/master by this push:
     new 466b7c5  Improve error message and comments (#641)
466b7c5 is described below

commit 466b7c5722b61f3328fb4ed91f4b11d050eb60ff
Author: Andrew Lamb <an...@nerdnetworks.org>
AuthorDate: Wed Jun 30 16:35:19 2021 -0400

    Improve error message and comments (#641)
---
 datafusion/src/logical_plan/dfschema.rs |  4 ++--
 datafusion/src/logical_plan/expr.rs     | 10 ++++++++--
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/datafusion/src/logical_plan/dfschema.rs b/datafusion/src/logical_plan/dfschema.rs
index b46e067..b4d864f 100644
--- a/datafusion/src/logical_plan/dfschema.rs
+++ b/datafusion/src/logical_plan/dfschema.rs
@@ -158,8 +158,8 @@ impl DFSchema {
             }
         }
         Err(DataFusionError::Plan(format!(
-            "No field matches column '{}'",
-            col,
+            "No field matches column '{}'. Available fields: {}",
+            col, self
         )))
     }
 
diff --git a/datafusion/src/logical_plan/expr.rs b/datafusion/src/logical_plan/expr.rs
index 1bf3b65..1fab9bb 100644
--- a/datafusion/src/logical_plan/expr.rs
+++ b/datafusion/src/logical_plan/expr.rs
@@ -83,7 +83,12 @@ impl Column {
         }
     }
 
-    /// Normalize Column with qualifier based on provided dataframe schemas.
+    /// Normalizes `self` if is unqualified (has no relation name)
+    /// with an explicit qualifier from the first matching input
+    /// schemas.
+    ///
+    /// For example, `foo` will be normalized to `t.foo` if there is a
+    /// column named `foo` in a relation named `t` found in `schemas`
     pub fn normalize(self, schemas: &[&DFSchemaRef]) -> Result<Self> {
         if self.relation.is_some() {
             return Ok(self);
@@ -1113,7 +1118,8 @@ pub fn columnize_expr(e: Expr, input_schema: &DFSchema) -> Expr {
     }
 }
 
-/// Recursively normalize all Column expressions in a given expression tree
+/// Recursively call [`Column::normalize`] on all Column expressions
+/// in the `expr` expression tree.
 pub fn normalize_col(e: Expr, schemas: &[&DFSchemaRef]) -> Result<Expr> {
     struct ColumnNormalizer<'a, 'b> {
         schemas: &'a [&'b DFSchemaRef],