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ARROW-7268: [Rust] Add custom_metadata field from IPC message to Schema. #5907

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ARROW-7268: [Rust] Add custom_metadata field from IPC message to Schema. #5907

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216 changes: 165 additions & 51 deletions rust/arrow/src/datatypes.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@
//! information regarding data-types and memory layouts see
//! [here](https://arrow.apache.org/docs/memory_layout.html).

use std::collections::HashMap;
use std::fmt;
use std::mem::size_of;
#[cfg(feature = "simd")]
Expand Down Expand Up @@ -901,12 +902,18 @@ impl fmt::Display for Field {
#[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(default)]
pub(crate) metadata: HashMap<String, String>,
}

impl Schema {
/// Creates an empty `Schema`
pub fn empty() -> Self {
Self { fields: vec![] }
Self {
fields: vec![],
metadata: HashMap::new(),
}
}

/// Creates a new `Schema` from a sequence of `Field` values
Expand All @@ -922,7 +929,30 @@ impl Schema {
/// let schema = Schema::new(vec![field_a, field_b]);
/// ```
pub fn new(fields: Vec<Field>) -> Self {
Self { fields }
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
///
/// ```
/// # extern crate arrow;
/// # 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);
/// ```
pub fn new_with_metadata(
fields: Vec<Field>,
metadata: HashMap<String, String>,
) -> Self {
Self { fields, metadata }
}

/// Returns an immutable reference of the vector of `Field` instances
Expand All @@ -936,6 +966,11 @@ impl Schema {
&self.fields[i]
}

/// Returns an immutable reference to the Map of custom metadata key-value pairs.
pub fn metadata(&self) -> &HashMap<String, String> {
&self.metadata
}

/// Look up a column by name and return a immutable reference to the column along with
/// it's index
pub fn column_with_name(&self, name: &str) -> Option<(usize, &Field)> {
Expand All @@ -949,28 +984,59 @@ impl 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) => {
if let Some(Value::Array(fields)) = schema.get("fields") {
let fields: Result<Vec<Field>> =
fields.iter().map(|f| Field::from(f)).collect();
Ok(Schema::new(fields?))
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
fn from_metadata(json: &Value) -> Result<HashMap<String, String>> {
if let Value::Object(md) = json {
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<_>>()
} else {
Err(ArrowError::ParseError(
"`metadata` field must be an object".to_string(),
))
}
}
}

impl fmt::Display for Schema {
Expand Down Expand Up @@ -1171,49 +1237,59 @@ mod tests {

#[test]
fn schema_json() {
let schema = Schema::new(vec![
Field::new("c1", DataType::Utf8, false),
Field::new("c2", DataType::Binary, false),
Field::new("c3", DataType::FixedSizeBinary(3), false),
Field::new("c4", DataType::Boolean, false),
Field::new("c5", DataType::Date32(DateUnit::Day), false),
Field::new("c6", DataType::Date64(DateUnit::Millisecond), false),
Field::new("c7", DataType::Time32(TimeUnit::Second), false),
Field::new("c8", DataType::Time32(TimeUnit::Millisecond), false),
Field::new("c9", DataType::Time32(TimeUnit::Microsecond), false),
Field::new("c10", DataType::Time32(TimeUnit::Nanosecond), false),
Field::new("c11", DataType::Time64(TimeUnit::Second), false),
Field::new("c12", DataType::Time64(TimeUnit::Millisecond), false),
Field::new("c13", DataType::Time64(TimeUnit::Microsecond), false),
Field::new("c14", DataType::Time64(TimeUnit::Nanosecond), false),
Field::new("c15", DataType::Timestamp(TimeUnit::Second), false),
Field::new("c16", DataType::Timestamp(TimeUnit::Millisecond), false),
Field::new("c17", DataType::Timestamp(TimeUnit::Microsecond), false),
Field::new("c18", DataType::Timestamp(TimeUnit::Nanosecond), false),
Field::new("c19", DataType::Interval(IntervalUnit::DayTime), false),
Field::new("c20", DataType::Interval(IntervalUnit::YearMonth), false),
Field::new("c21", DataType::List(Box::new(DataType::Boolean)), false),
Field::new(
"c22",
DataType::FixedSizeList((Box::new(DataType::Boolean), 5)),
false,
),
Field::new(
"c23",
DataType::List(Box::new(DataType::List(Box::new(DataType::Struct(
vec![],
))))),
true,
),
Field::new(
"c24",
DataType::Struct(vec![
Field::new("a", DataType::Utf8, false),
Field::new("b", DataType::UInt16, false),
]),
false,
),
]);
// Add some custom metadata
let metadata: HashMap<String, String> =
[("Key".to_string(), "Value".to_string())]
.iter()
.cloned()
.collect();

let schema = Schema::new_with_metadata(
vec![
Field::new("c1", DataType::Utf8, false),
Field::new("c2", DataType::Binary, false),
Field::new("c3", DataType::FixedSizeBinary(3), false),
Field::new("c4", DataType::Boolean, false),
Field::new("c5", DataType::Date32(DateUnit::Day), false),
Field::new("c6", DataType::Date64(DateUnit::Millisecond), false),
Field::new("c7", DataType::Time32(TimeUnit::Second), false),
Field::new("c8", DataType::Time32(TimeUnit::Millisecond), false),
Field::new("c9", DataType::Time32(TimeUnit::Microsecond), false),
Field::new("c10", DataType::Time32(TimeUnit::Nanosecond), false),
Field::new("c11", DataType::Time64(TimeUnit::Second), false),
Field::new("c12", DataType::Time64(TimeUnit::Millisecond), false),
Field::new("c13", DataType::Time64(TimeUnit::Microsecond), false),
Field::new("c14", DataType::Time64(TimeUnit::Nanosecond), false),
Field::new("c15", DataType::Timestamp(TimeUnit::Second), false),
Field::new("c16", DataType::Timestamp(TimeUnit::Millisecond), false),
Field::new("c17", DataType::Timestamp(TimeUnit::Microsecond), false),
Field::new("c18", DataType::Timestamp(TimeUnit::Nanosecond), false),
Field::new("c19", DataType::Interval(IntervalUnit::DayTime), false),
Field::new("c20", DataType::Interval(IntervalUnit::YearMonth), false),
Field::new("c21", DataType::List(Box::new(DataType::Boolean)), false),
Field::new(
"c22",
DataType::FixedSizeList((Box::new(DataType::Boolean), 5)),
false,
),
Field::new(
"c23",
DataType::List(Box::new(DataType::List(Box::new(DataType::Struct(
vec![],
))))),
true,
),
Field::new(
"c24",
DataType::Struct(vec![
Field::new("a", DataType::Utf8, false),
Field::new("b", DataType::UInt16, false),
]),
false,
),
],
metadata,
);

let expected = schema.to_json();
let json = r#"{
Expand Down Expand Up @@ -1491,7 +1567,10 @@ mod tests {
}
]
}
]
],
"metadata" : {
"Key": "Value"
}
}"#;
let value: Value = serde_json::from_str(&json).unwrap();
assert_eq!(expected, value);
Expand All @@ -1501,6 +1580,41 @@ mod tests {
let schema2 = Schema::from(&value).unwrap();

assert_eq!(schema, schema2);

// Check that empty metadata produces empty value in JSON and can be parsed
let json = r#"{
"fields": [
{
"name": "c1",
"nullable": false,
"type": {
"name": "utf8"
},
"children": []
}
],
"metadata": {}
}"#;
let value: Value = serde_json::from_str(&json).unwrap();
let schema = Schema::from(&value).unwrap();
assert!(schema.metadata.is_empty());

// Check that metadata field is not required in the JSON.
let json = r#"{
"fields": [
{
"name": "c1",
"nullable": false,
"type": {
"name": "utf8"
},
"children": []
}
]
}"#;
let value: Value = serde_json::from_str(&json).unwrap();
let schema = Schema::from(&value).unwrap();
assert!(schema.metadata.is_empty());
}

#[test]
Expand Down
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