mentat/core/src/lib.rs

// Copyright 2016 Mozilla
//
// Licensed 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.

extern crate ordered_float;
use self::ordered_float::OrderedFloat;

/// Core types defining a Mentat knowledge base.

/// Represents one entid in the entid space.
///
/// Per https://www.sqlite.org/datatype3.html (see also http://stackoverflow.com/a/8499544), SQLite
/// stores signed integers up to 64 bits in size.  Since u32 is not appropriate for our use case, we
/// use i64 rather than manually truncating u64 to u63 and casting to i64 throughout the codebase.
pub type Entid = i64;

/// The attribute of each Mentat assertion has a :db/valueType constraining the value to a
/// particular set.  Mentat recognizes the following :db/valueType values.
#[derive(Clone,Debug,Eq,Hash,Ord,PartialOrd,PartialEq)]
pub enum ValueType {
    Ref,
    Boolean,
    Instant,
    Long,
    Double,
    String,
    Keyword,
}

/// Represents a Mentat value in a particular value set.
// TODO: expand to include :db.type/{instant,url,uuid}.
// TODO: BigInt?
#[derive(Clone,Debug,Eq,Hash,Ord,PartialOrd,PartialEq)]
pub enum TypedValue {
    Ref(Entid),
    Boolean(bool),
    Long(i64),
    Double(OrderedFloat<f64>),
    // TODO: &str throughout?
    String(String),
    Keyword(String),
}

impl TypedValue {
    pub fn value_type(&self) -> ValueType {
        match self {
            &TypedValue::Ref(_) => ValueType::Ref,
            &TypedValue::Boolean(_) => ValueType::Boolean,
            &TypedValue::Long(_) => ValueType::Long,
            &TypedValue::Double(_) => ValueType::Double,
            &TypedValue::String(_) => ValueType::String,
            &TypedValue::Keyword(_) => ValueType::Keyword,
        }
    }
}

/// A Mentat schema attribute has a value type and several other flags determining how assertions
/// with the attribute are interpreted.
///
/// TODO: consider packing this into a bitfield or similar.
#[derive(Clone,Debug,Eq,Hash,Ord,PartialOrd,PartialEq)]
pub struct Attribute {
    /// The associated value type, i.e., `:db/valueType`?
    pub value_type: ValueType,

    /// `true` if this attribute is multi-valued, i.e., it is `:db/cardinality
    /// :db.cardinality/many`.  `false` if this attribute is single-valued (the default), i.e., it
    /// is `:db/cardinality :db.cardinality/one`.
    pub multival: bool,

    /// `true` if this attribute is unique-value, i.e., it is `:db/unique :db.unique/value`.
    ///
    /// *Unique-value* means that there is at most one assertion with the attribute and a
    /// particular value in the datom store.
    pub unique_value: bool,

    /// `true` if this attribute is unique-identity, i.e., it is `:db/unique :db.unique/identity`.
    ///
    /// Unique-identity attributes always have value type `Ref`.
    ///
    /// *Unique-identity* means that the attribute is *unique-value* and that they can be used in
    /// lookup-refs and will automatically upsert where appropriate.
    pub unique_identity: bool,

    /// `true` if this attribute is automatically indexed, i.e., it is `:db/indexing true`.
    pub index: bool,

    /// `true` if this attribute is automatically fulltext indexed, i.e., it is `:db/fulltext true`.
    ///
    /// Fulltext attributes always have string values.
    pub fulltext: bool,

    /// `true` if this attribute is a component, i.e., it is `:db/isComponent true`.
    ///
    /// Component attributes always have value type `Ref`.
    ///
    /// They are used to compose entities from component sub-entities: they are fetched recursively
    /// by pull expressions, and they are automatically recursively deleted where appropriate.
    pub component: bool,
}

impl Default for Attribute {
    fn default() -> Attribute {
        Attribute {
            // There's no particular reason to favour one value type, so Ref it is.
            value_type: ValueType::Ref,
            fulltext: false,
            index: false,
            multival: false,
            unique_value: false,
            unique_identity: false,
            component: false,
        }
    }
}