[GitHub] [arrow] andygrove commented on a change in pull request #8840: ARROW-10813: [Rust] [DataFusion] Implement DFSchema

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

andygrove commented on a change in pull request #8840:
URL: https://github.com/apache/arrow/pull/8840#discussion_r537054293



##########
File path: rust/datafusion/src/logical_plan/dfschema.rs
##########
@@ -0,0 +1,415 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! DFSchema is an extended schema struct that DataFusion uses to provide support for
+//! fields with optional relation names.
+
+use std::collections::HashSet;
+use std::sync::Arc;
+
+use crate::error::{DataFusionError, Result};
+
+use arrow::datatypes::{DataType, Field, Schema, SchemaRef};
+use std::fmt::{Display, Formatter};
+
+/// A reference-counted reference to a `DFSchema`.
+pub type DFSchemaRef = Arc<DFSchema>;
+
+/// DFSchema wraps an Arrow schema and adds relation names
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct DFSchema {
+    /// Fields
+    fields: Vec<DFField>,
+}
+
+impl DFSchema {
+    /// Creates an empty `DFSchema`
+    pub fn empty() -> Self {
+        Self { fields: vec![] }
+    }
+
+    /// Create a new `DFSchema`
+    pub fn new(fields: Vec<DFField>) -> Result<Self> {
+        let mut qualified_names: HashSet<(&str, &str)> = HashSet::new();
+        let mut unqualified_names: HashSet<&str> = HashSet::new();
+        for field in &fields {
+            if let Some(qualifier) = field.qualifier() {
+                if !qualified_names.insert((qualifier, field.name())) {
+                    return Err(DataFusionError::Plan(format!(
+                        "Joined schema would contain duplicate qualified field name '{}'",
+                        field.qualified_name()
+                    )));
+                }
+            } else {
+                if !unqualified_names.insert(field.name()) {
+                    return Err(DataFusionError::Plan(
+                        format!("Joined schema would contain duplicate unqualified field name '{}'",
+                                field.name())
+                    ));
+                }
+            }
+        }
+
+        // check for mix of qualified and unqualified field with same unqualified name
+        // note that we need to sort the contents of the HashSet first so that errors are
+        // deterministic
+        let mut qualified_names: Vec<&(&str, &str)> = qualified_names.iter().collect();
+        qualified_names.sort_by(|a, b| {
+            let a = format!("{}.{}", a.0, a.1);
+            let b = format!("{}.{}", b.0, b.1);
+            a.cmp(&b)
+        });
+        for (qualifier, name) in &qualified_names {
+            if unqualified_names.contains(name) {
+                return Err(DataFusionError::Plan(format!(
+                    "Joined schema would contain qualified field name '{}.{}' \
+                    and unqualified field name '{}' which would be ambiguous",
+                    qualifier, name, name
+                )));
+            }
+        }
+        Ok(Self { fields })
+    }
+
+    /// Create a `DFSchema` from an Arrow schema
+    pub fn from(schema: &Schema) -> Result<Self> {
+        Self::new(
+            schema
+                .fields()
+                .iter()
+                .map(|f| DFField {
+                    field: f.clone(),
+                    qualifier: None,
+                })
+                .collect(),
+        )
+    }
+
+    /// Create a `DFSchema` from an Arrow schema
+    pub fn from_qualified(qualifier: &str, schema: &Schema) -> Result<Self> {
+        Self::new(
+            schema
+                .fields()
+                .iter()
+                .map(|f| DFField {
+                    field: f.clone(),
+                    qualifier: Some(qualifier.to_owned()),
+                })
+                .collect(),
+        )
+    }
+
+    /// Combine two schemas
+    pub fn join(&self, schema: &DFSchema) -> Result<Self> {
+        let mut fields = self.fields.clone();
+        fields.extend_from_slice(schema.fields().as_slice());
+        Self::new(fields)
+    }
+
+    /// Get a list of fields
+    pub fn fields(&self) -> &Vec<DFField> {
+        &self.fields
+    }
+
+    /// Returns an immutable reference of a specific `Field` instance selected using an
+    /// offset within the internal `fields` vector
+    pub fn field(&self, i: usize) -> &DFField {
+        &self.fields[i]
+    }
+
+    /// Find the index of the column with the given name
+    pub fn index_of(&self, name: &str) -> Result<usize> {
+        for i in 0..self.fields.len() {
+            if self.fields[i].name() == name {
+                return Ok(i);
+            }
+        }
+        Err(DataFusionError::Plan(format!("No field named '{}'", name)))
+    }
+
+    /// Find the field with the given name
+    pub fn field_with_name(
+        &self,
+        relation_name: Option<&str>,
+        name: &str,
+    ) -> Result<DFField> {
+        if let Some(relation_name) = relation_name {
+            self.field_with_qualified_name(relation_name, name)
+        } else {
+            self.field_with_unqualified_name(name)
+        }
+    }
+
+    /// Find the field with the given name
+    pub fn field_with_unqualified_name(&self, name: &str) -> Result<DFField> {
+        let matches: Vec<&DFField> = self
+            .fields
+            .iter()
+            .filter(|field| field.name() == name)
+            .collect();
+        match matches.len() {
+            0 => Err(DataFusionError::Plan(format!("No field named '{}'", name))),
+            1 => Ok(matches[0].to_owned()),
+            _ => Err(DataFusionError::Plan(format!(
+                "Ambiguous reference to field named '{}'",
+                name
+            ))),
+        }
+    }
+
+    /// Find the field with the given qualified name
+    pub fn field_with_qualified_name(
+        &self,
+        relation_name: &str,
+        name: &str,
+    ) -> Result<DFField> {
+        let matches: Vec<&DFField> = self
+            .fields
+            .iter()
+            .filter(|field| {
+                field.qualifier == Some(relation_name.to_string()) && field.name() == name
+            })
+            .collect();
+        match matches.len() {
+            0 => Err(DataFusionError::Plan(format!(
+                "No field named '{}.{}'",
+                relation_name, name
+            ))),
+            1 => Ok(matches[0].to_owned()),
+            _ => Err(DataFusionError::Plan(format!(
+                "Ambiguous reference to qualified field named '{}.{}'",
+                relation_name, name
+            ))),
+        }
+    }
+
+    /// Convert to an Arrow schema
+    pub fn to_arrow_schema(&self) -> SchemaRef {
+        SchemaRef::new(Schema::new(
+            self.fields.iter().map(|f| f.field.clone()).collect(),
+        ))
+    }
+}
+
+impl Display for DFSchema {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "{}",
+            self.fields
+                .iter()
+                .map(|field| field.qualified_name())
+                .collect::<Vec<String>>()
+                .join(", ")
+        )
+    }
+}
+
+/// DFField wraps an Arrow field and adds an optional qualifier
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct DFField {
+    /// Optional qualifier (usually a table or relation name)
+    qualifier: Option<String>,
+    /// Arrow field definition
+    field: Field,
+}
+
+impl DFField {
+    /// Creates a new `DFField`
+    pub fn new(
+        qualifier: Option<&str>,
+        name: &str,
+        data_type: DataType,
+        nullable: bool,
+    ) -> Self {
+        DFField {
+            qualifier: qualifier.map(|s| s.to_owned()),
+            field: Field::new(name, data_type, nullable),
+        }
+    }
+
+    /// Create an unqualified field from an existing Arrow field
+    pub fn from(field: Field) -> Self {
+        Self {
+            qualifier: None,
+            field,
+        }
+    }
+
+    /// Create a qualified field from an existing Arrow field
+    pub fn from_qualified(qualifier: &str, field: Field) -> Self {
+        Self {
+            qualifier: Some(qualifier.to_owned()),
+            field,
+        }
+    }
+
+    /// Returns an immutable reference to the `DFField`'s unqualified name
+    pub fn name(&self) -> &String {
+        &self.field.name()
+    }
+
+    /// Returns an immutable reference to the `DFField`'s data-type
+    pub fn data_type(&self) -> &DataType {
+        &self.field.data_type()
+    }
+
+    /// Indicates whether this `DFField` supports null values
+    pub fn is_nullable(&self) -> bool {
+        self.field.is_nullable()
+    }
+
+    /// Returns an immutable reference to the `DFField`'s qualified name

Review comment:
       Thanks. I have copy and pasted the comments from Arrow's Field and will update the comment here.




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