fosk 0.1.14

In-memory SQL-like query engine and lightweight data store for testing and prototyping.
Documentation 
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use serde::{Deserialize, Serialize};
use serde_json::Value;

use crate::JsonPrimitive;

/// Metadata for a single field inferred from JSON documents.
///
/// - `ty`: the coarse-grained primitive type of the field.
/// - `nullable`: whether the field was observed as `null` or missing in any
///   analyzed document.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct FieldInfo {
    /// Primitive type of the field
    pub ty: JsonPrimitive,
    /// Whether the field may be null / missing
    pub nullable: bool,
}

impl FieldInfo {
    /// Infer a `FieldInfo` from a single `serde_json::Value`.
    ///
    /// If the value is `null` the returned `FieldInfo` will have `nullable = true`.
    ///
    /// # Example
    ///
    /// ```
    /// use fosk::{FieldInfo, JsonPrimitive};
    /// use serde_json::json;
    ///
    /// let info = FieldInfo::infer_field_info(&json!("Ada"));
    ///
    /// assert_eq!(info.ty, JsonPrimitive::String);
    /// assert!(!info.nullable);
    /// ```
    pub fn infer_field_info(value: &Value) -> FieldInfo {
        let ty = JsonPrimitive::of_value(value);
        FieldInfo {
            ty: if ty == JsonPrimitive::Null {
                JsonPrimitive::Null
            } else {
                ty
            },
            nullable: ty == JsonPrimitive::Null,
        }
    }

    /// Merge this `FieldInfo` with another observation returning the promoted
    /// result. Promotion handles numeric widening (Int -> Float) and
    /// preserves nullability if either side is nullable.
    ///
    /// # Example
    ///
    /// ```
    /// use fosk::{FieldInfo, JsonPrimitive};
    /// use serde_json::json;
    ///
    /// let int_info = FieldInfo::infer_field_info(&json!(1));
    /// let float_info = FieldInfo::infer_field_info(&json!(1.5));
    ///
    /// let merged = int_info.merge_field_info(&float_info);
    ///
    /// assert_eq!(merged.ty, JsonPrimitive::Float);
    /// ```
    pub fn merge_field_info(&self, new: &FieldInfo) -> FieldInfo {
        let promoted = JsonPrimitive::promote(self.ty, new.ty);
        FieldInfo {
            ty: if promoted == JsonPrimitive::Null {
                self.ty
            } else {
                promoted
            },
            nullable: self.nullable || new.nullable || new.ty == JsonPrimitive::Null,
        }
    }
}

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

    #[test]
    fn test_type_promotion_int_to_float() {
        let a = FieldInfo {
            ty: JsonPrimitive::Int,
            nullable: false,
        };
        let b = FieldInfo {
            ty: JsonPrimitive::Float,
            nullable: false,
        };
        let c = a.merge_field_info(&b);
        assert_eq!(c.ty, JsonPrimitive::Float);
        assert!(!c.nullable);
    }
}