deltalake_core/kernel/models/
schema.rs

//! Delta table schema

use std::sync::Arc;

pub use delta_kernel::schema::{
    ArrayType, ColumnMetadataKey, DataType, MapType, MetadataValue, PrimitiveType, StructField,
    StructType,
};
use serde_json::Value;

use crate::kernel::error::Error;
use crate::kernel::DataCheck;

/// Type alias for a top level schema
pub type Schema = StructType;
/// Schema reference type
pub type SchemaRef = Arc<StructType>;

/// An invariant for a column that is enforced on all writes to a Delta table.
#[derive(Eq, PartialEq, Debug, Default, Clone)]
pub struct Invariant {
    /// The full path to the field.
    pub field_name: String,
    /// The SQL string that must always evaluate to true.
    pub invariant_sql: String,
}

impl Invariant {
    /// Create a new invariant
    pub fn new(field_name: &str, invariant_sql: &str) -> Self {
        Self {
            field_name: field_name.to_string(),
            invariant_sql: invariant_sql.to_string(),
        }
    }
}

impl DataCheck for Invariant {
    fn get_name(&self) -> &str {
        &self.field_name
    }

    fn get_expression(&self) -> &str {
        &self.invariant_sql
    }
}

/// Trait to add convenince functions to struct type
pub trait StructTypeExt {
    /// Get all invariants in the schemas
    fn get_invariants(&self) -> Result<Vec<Invariant>, Error>;
}

impl StructTypeExt for StructType {
    /// Get all invariants in the schemas
    fn get_invariants(&self) -> Result<Vec<Invariant>, Error> {
        let mut remaining_fields: Vec<(String, StructField)> = self
            .fields()
            .map(|field| (field.name.clone(), field.clone()))
            .collect();
        let mut invariants: Vec<Invariant> = Vec::new();

        let add_segment = |prefix: &str, segment: &str| -> String {
            if prefix.is_empty() {
                segment.to_owned()
            } else {
                format!("{prefix}.{segment}")
            }
        };

        while let Some((field_path, field)) = remaining_fields.pop() {
            match field.data_type() {
                DataType::Struct(inner) => {
                    remaining_fields.extend(
                        inner
                            .fields()
                            .map(|field| {
                                let new_prefix = add_segment(&field_path, &field.name);
                                (new_prefix, field.clone())
                            })
                            .collect::<Vec<(String, StructField)>>(),
                    );
                }
                DataType::Array(inner) => {
                    let element_field_name = add_segment(&field_path, "element");
                    remaining_fields.push((
                        element_field_name,
                        StructField::new("".to_string(), inner.element_type.clone(), false),
                    ));
                }
                DataType::Map(inner) => {
                    let key_field_name = add_segment(&field_path, "key");
                    remaining_fields.push((
                        key_field_name,
                        StructField::new("".to_string(), inner.key_type.clone(), false),
                    ));
                    let value_field_name = add_segment(&field_path, "value");
                    remaining_fields.push((
                        value_field_name,
                        StructField::new("".to_string(), inner.value_type.clone(), false),
                    ));
                }
                _ => {}
            }
            // JSON format: {"expression": {"expression": "<SQL STRING>"} }
            if let Some(MetadataValue::String(invariant_json)) =
                field.metadata.get(ColumnMetadataKey::Invariants.as_ref())
            {
                let json: Value = serde_json::from_str(invariant_json).map_err(|e| {
                    Error::InvalidInvariantJson {
                        json_err: e,
                        line: invariant_json.to_string(),
                    }
                })?;
                if let Value::Object(json) = json {
                    if let Some(Value::Object(expr1)) = json.get("expression") {
                        if let Some(Value::String(sql)) = expr1.get("expression") {
                            invariants.push(Invariant::new(&field_path, sql));
                        }
                    }
                }
            }
        }
        Ok(invariants)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use serde_json;
    use serde_json::json;

    #[test]
    fn test_get_invariants() {
        let schema: StructType = serde_json::from_value(json!({
            "type": "struct",
            "fields": [{"name": "x", "type": "string", "nullable": true, "metadata": {}}]
        }))
        .unwrap();
        let invariants = schema.get_invariants().unwrap();
        assert_eq!(invariants.len(), 0);

        let schema: StructType = serde_json::from_value(json!({
            "type": "struct",
            "fields": [
                {"name": "x", "type": "integer", "nullable": true, "metadata": {
                    "delta.invariants": "{\"expression\": { \"expression\": \"x > 2\"} }"
                }},
                {"name": "y", "type": "integer", "nullable": true, "metadata": {
                    "delta.invariants": "{\"expression\": { \"expression\": \"y < 4\"} }"
                }}
            ]
        }))
        .unwrap();
        let invariants = schema.get_invariants().unwrap();
        assert_eq!(invariants.len(), 2);
        assert!(invariants.contains(&Invariant::new("x", "x > 2")));
        assert!(invariants.contains(&Invariant::new("y", "y < 4")));

        let schema: StructType = serde_json::from_value(json!({
            "type": "struct",
            "fields": [{
                "name": "a_map",
                "type": {
                    "type": "map",
                    "keyType": "string",
                    "valueType": {
                        "type": "array",
                        "elementType": {
                            "type": "struct",
                            "fields": [{
                                "name": "d",
                                "type": "integer",
                                "metadata": {
                                    "delta.invariants": "{\"expression\": { \"expression\": \"a_map.value.element.d < 4\"} }"
                                },
                                "nullable": false
                            }]
                        },
                        "containsNull": false
                    },
                    "valueContainsNull": false
                },
                "nullable": false,
                "metadata": {}
            }]
        })).unwrap();
        let invariants = schema.get_invariants().unwrap();
        assert_eq!(invariants.len(), 1);
        assert_eq!(
            invariants[0],
            Invariant::new("a_map.value.element.d", "a_map.value.element.d < 4")
        );
    }

    /// <https://github.com/delta-io/delta-rs/issues/2152>
    #[test]
    fn test_identity_columns() {
        let buf = r#"{"type":"struct","fields":[{"name":"ID_D_DATE","type":"long","nullable":true,"metadata":{"delta.identity.start":1,"delta.identity.step":1,"delta.identity.allowExplicitInsert":false}},{"name":"TXT_DateKey","type":"string","nullable":true,"metadata":{}}]}"#;
        let _schema: StructType = serde_json::from_str(buf).expect("Failed to load");
    }
}
deltalake_core/kernel/models/schema.rs

deltalake_core/kernel/models/
schema.rs
