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// 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.
use std::collections::HashMap;
use std::default::Default;
use std::fmt;
use serde_derive::{Deserialize, Serialize};
use serde_json::{json, Value};
use crate::error::{ArrowError, Result};
use super::Field;
/// Describes the meta-data of an ordered sequence of relative types.
///
/// Note that this information is only part of the meta-data and not part of the physical
/// memory layout.
#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
pub struct Schema {
pub(crate) fields: Vec<Field>,
/// A map of key-value pairs containing additional meta data.
#[serde(skip_serializing_if = "HashMap::is_empty")]
#[serde(default)]
pub(crate) metadata: HashMap<String, String>,
}
impl Schema {
/// Creates an empty `Schema`
pub fn empty() -> Self {
Self {
fields: vec![],
metadata: HashMap::new(),
}
}
/// Creates a new `Schema` from a sequence of `Field` values.
///
/// # Example
///
/// ```
/// # use arrow::datatypes::{Field, DataType, Schema};
/// let field_a = Field::new("a", DataType::Int64, false);
/// let field_b = Field::new("b", DataType::Boolean, false);
///
/// let schema = Schema::new(vec![field_a, field_b]);
/// ```
pub fn new(fields: Vec<Field>) -> Self {
Self::new_with_metadata(fields, HashMap::new())
}
/// Creates a new `Schema` from a sequence of `Field` values
/// and adds additional metadata in form of key value pairs.
///
/// # Example
///
/// ```
/// # use arrow::datatypes::{Field, DataType, Schema};
/// # use std::collections::HashMap;
/// let field_a = Field::new("a", DataType::Int64, false);
/// let field_b = Field::new("b", DataType::Boolean, false);
///
/// let mut metadata: HashMap<String, String> = HashMap::new();
/// metadata.insert("row_count".to_string(), "100".to_string());
///
/// let schema = Schema::new_with_metadata(vec![field_a, field_b], metadata);
/// ```
#[inline]
pub const fn new_with_metadata(
fields: Vec<Field>,
metadata: HashMap<String, String>,
) -> Self {
Self { fields, metadata }
}
/// Merge schema into self if it is compatible. Struct fields will be merged recursively.
///
/// Example:
///
/// ```
/// use arrow::datatypes::*;
///
/// let merged = Schema::try_merge(vec![
/// Schema::new(vec![
/// Field::new("c1", DataType::Int64, false),
/// Field::new("c2", DataType::Utf8, false),
/// ]),
/// Schema::new(vec![
/// Field::new("c1", DataType::Int64, true),
/// Field::new("c2", DataType::Utf8, false),
/// Field::new("c3", DataType::Utf8, false),
/// ]),
/// ]).unwrap();
///
/// assert_eq!(
/// merged,
/// Schema::new(vec![
/// Field::new("c1", DataType::Int64, true),
/// Field::new("c2", DataType::Utf8, false),
/// Field::new("c3", DataType::Utf8, false),
/// ]),
/// );
/// ```
pub fn try_merge(schemas: impl IntoIterator<Item = Self>) -> Result<Self> {
schemas
.into_iter()
.try_fold(Self::empty(), |mut merged, schema| {
let Schema { metadata, fields } = schema;
for (key, value) in metadata.into_iter() {
// merge metadata
if let Some(old_val) = merged.metadata.get(&key) {
if old_val != &value {
return Err(ArrowError::SchemaError(
"Fail to merge schema due to conflicting metadata."
.to_string(),
));
}
}
merged.metadata.insert(key, value);
}
// merge fields
for field in fields.into_iter() {
let mut new_field = true;
for merged_field in &mut merged.fields {
if field.name() != merged_field.name() {
continue;
}
new_field = false;
merged_field.try_merge(&field)?
}
// found a new field, add to field list
if new_field {
merged.fields.push(field);
}
}
Ok(merged)
})
}
/// Returns an immutable reference of the vector of `Field` instances.
#[inline]
pub const fn fields(&self) -> &Vec<Field> {
&self.fields
}
/// Returns a vector with references to all fields (including nested fields)
#[inline]
pub(crate) fn all_fields(&self) -> Vec<&Field> {
self.fields.iter().map(|f| f.fields()).flatten().collect()
}
/// Returns an immutable reference of a specific `Field` instance selected using an
/// offset within the internal `fields` vector.
pub fn field(&self, i: usize) -> &Field {
&self.fields[i]
}
/// Returns an immutable reference of a specific `Field` instance selected by name.
pub fn field_with_name(&self, name: &str) -> Result<&Field> {
Ok(&self.fields[self.index_of(name)?])
}
/// Returns a vector of immutable references to all `Field` instances selected by
/// the dictionary ID they use.
pub fn fields_with_dict_id(&self, dict_id: i64) -> Vec<&Field> {
self.fields
.iter()
.map(|f| f.fields_with_dict_id(dict_id))
.flatten()
.collect()
}
/// 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);
}
}
let valid_fields: Vec<String> =
self.fields.iter().map(|f| f.name().clone()).collect();
Err(ArrowError::InvalidArgumentError(format!(
"Unable to get field named \"{}\". Valid fields: {:?}",
name, valid_fields
)))
}
/// Returns an immutable reference to the Map of custom metadata key-value pairs.
#[inline]
pub const fn metadata(&self) -> &HashMap<String, String> {
&self.metadata
}
/// Look up a column by name and return a immutable reference to the column along with
/// its index.
pub fn column_with_name(&self, name: &str) -> Option<(usize, &Field)> {
self.fields
.iter()
.enumerate()
.find(|&(_, c)| c.name() == name)
}
/// Generate a JSON representation of the `Schema`.
pub fn to_json(&self) -> Value {
json!({
"fields": self.fields.iter().map(|field| field.to_json()).collect::<Vec<Value>>(),
"metadata": serde_json::to_value(&self.metadata).unwrap()
})
}
/// Parse a `Schema` definition from a JSON representation.
pub fn from(json: &Value) -> Result<Self> {
match *json {
Value::Object(ref schema) => {
let fields = if let Some(Value::Array(fields)) = schema.get("fields") {
fields
.iter()
.map(|f| Field::from(f))
.collect::<Result<_>>()?
} else {
return Err(ArrowError::ParseError(
"Schema fields should be an array".to_string(),
));
};
let metadata = if let Some(value) = schema.get("metadata") {
Self::from_metadata(value)?
} else {
HashMap::default()
};
Ok(Self { fields, metadata })
}
_ => Err(ArrowError::ParseError(
"Invalid json value type for schema".to_string(),
)),
}
}
/// Parse a `metadata` definition from a JSON representation.
/// The JSON can either be an Object or an Array of Objects.
fn from_metadata(json: &Value) -> Result<HashMap<String, String>> {
match json {
Value::Array(_) => {
let mut hashmap = HashMap::new();
let values: Vec<MetadataKeyValue> = serde_json::from_value(json.clone())
.map_err(|_| {
ArrowError::JsonError(
"Unable to parse object into key-value pair".to_string(),
)
})?;
for meta in values {
hashmap.insert(meta.key.clone(), meta.value);
}
Ok(hashmap)
}
Value::Object(md) => md
.iter()
.map(|(k, v)| {
if let Value::String(v) = v {
Ok((k.to_string(), v.to_string()))
} else {
Err(ArrowError::ParseError(
"metadata `value` field must be a string".to_string(),
))
}
})
.collect::<Result<_>>(),
_ => Err(ArrowError::ParseError(
"`metadata` field must be an object".to_string(),
)),
}
}
/// Check to see if `self` is a superset of `other` schema. Here are the comparision rules:
///
/// * `self` and `other` should contain the same number of fields
/// * for every field `f` in `other`, the field in `self` with corresponding index should be a
/// superset of `f`.
/// * self.metadata is a superset of other.metadata
///
/// In other words, any record conforms to `other` should also conform to `self`.
pub fn contains(&self, other: &Schema) -> bool {
if self.fields.len() != other.fields.len() {
return false;
}
for (i, field) in other.fields.iter().enumerate() {
if !self.fields[i].contains(field) {
return false;
}
}
// make sure self.metadata is a superset of other.metadata
for (k, v) in &other.metadata {
match self.metadata.get(k) {
Some(s) => {
if s != v {
return false;
}
}
None => {
return false;
}
}
}
true
}
}
impl fmt::Display for Schema {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.write_str(
&self
.fields
.iter()
.map(|c| c.to_string())
.collect::<Vec<String>>()
.join(", "),
)
}
}
#[derive(Deserialize)]
struct MetadataKeyValue {
key: String,
value: String,
}
#[cfg(test)]
mod tests {
use crate::datatypes::DataType;
use super::*;
#[test]
fn test_ser_de_metadata() {
// ser/de with empty metadata
let mut schema = Schema::new(vec![
Field::new("name", DataType::Utf8, false),
Field::new("address", DataType::Utf8, false),
Field::new("priority", DataType::UInt8, false),
]);
let json = serde_json::to_string(&schema).unwrap();
let de_schema = serde_json::from_str(&json).unwrap();
assert_eq!(schema, de_schema);
// ser/de with non-empty metadata
schema.metadata = [("key".to_owned(), "val".to_owned())]
.iter()
.cloned()
.collect();
let json = serde_json::to_string(&schema).unwrap();
let de_schema = serde_json::from_str(&json).unwrap();
assert_eq!(schema, de_schema);
}
}