Expose contents of Constraints (#7603)

Closes #7511

datafusion/common/src/functional_dependencies.rs

@@ -22,10 +22,11 @@ use crate::{DFSchema, DFSchemaRef, DataFusionError, JoinType, Result};
 use sqlparser::ast::TableConstraint;
 use std::collections::HashSet;
 use std::fmt::{Display, Formatter};
+use std::ops::Deref;
 
 /// This object defines a constraint on a table.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
-enum Constraint {
+pub enum Constraint {
     /// Columns with the given indices form a composite primary key (they are
     /// jointly unique and not nullable):
     PrimaryKey(Vec<usize>),
@@ -124,6 +125,14 @@ impl Display for Constraints {
     }
 }
 
+impl Deref for Constraints {
+    type Target = [Constraint];
+
+    fn deref(&self) -> &Self::Target {
+        self.inner.as_slice()
+    }
+}
+
 /// This object defines a functional dependence in the schema. A functional
 /// dependence defines a relationship between determinant keys and dependent
 /// columns. A determinant key is a column, or a set of columns, whose value
@@ -518,3 +527,20 @@ fn add_offset_to_vec<T: Copy + std::ops::Add<Output = T>>(
 ) -> Vec<T> {
     in_data.iter().map(|&item| item + offset).collect()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn constraints_iter() {
+        let constraints = Constraints::new(vec![
+            Constraint::PrimaryKey(vec![10]),
+            Constraint::Unique(vec![20]),
+        ]);
+        let mut iter = constraints.iter();
+        assert_eq!(iter.next(), Some(&Constraint::PrimaryKey(vec![10])));
+        assert_eq!(iter.next(), Some(&Constraint::Unique(vec![20])));
+        assert_eq!(iter.next(), None);
+    }
+}