Struct View 

pub struct View {
    pub name: String,
    /* private fields */
}

The View struct is Perspective’s query and serialization interface. It represents a query on the Table’s dataset and is always created from an existing Table instance via the Table::view method.

Views are immutable with respect to the arguments provided to the Table::view method; to change these parameters, you must create a new View on the same Table. However, each View is live with respect to the Table’s data, and will (within a conflation window) update with the latest state as its parent Table updates, including incrementally recalculating all aggregates, pivots, filters, etc. View query parameters are composable, in that each parameter works independently and in conjunction with each other, and there is no limit to the number of pivots, filters, etc. which can be applied.

To construct a View, call the Table::view factory method. A Table can have as many Views associated with it as you need - Perspective conserves memory by relying on a single Table to power multiple Views concurrently.

Examples

let opts = TableInitOptions::default();
let data = TableData::Update(UpdateData::Csv("x,y\n1,2\n3,4".into()));
let table = client.table(data, opts).await?;

let view = table.view(None).await?;
let arrow = view.to_arrow().await?;
view.delete().await?;

use crate::config::*;
let view = table
    .view(Some(ViewConfigUpdate {
        columns: Some(vec![Some("Sales".into())]),
        aggregates: Some(HashMap::from_iter(vec![("Sales".into(), "sum".into())])),
        group_by: Some(vec!["Region".into(), "Country".into()]),
        filter: Some(vec![Filter::new("Category", "in", &[
            "Furniture",
            "Technology",
        ])]),
        ..ViewConfigUpdate::default()
    }))
    .await?;

Group By

let view = table
    .view(Some(ViewConfigUpdate {
        group_by: Some(vec!["a".into(), "c".into()]),
        ..ViewConfigUpdate::default()
    }))
    .await?;

Split By

let view = table
    .view(Some(ViewConfigUpdate {
        split_by: Some(vec!["a".into(), "c".into()]),
        ..ViewConfigUpdate::default()
    }))
    .await?;

In Javascript, a Table can be constructed on a Table::view instance, which will return a new Table based on the Table::view’s dataset, and all future updates that affect the Table::view will be forwarded to the new Table. This is particularly useful for implementing a Client/Server Replicated design, by serializing the View to an arrow and setting up an on_update callback.

let opts = TableInitOptions::default();
let data = TableData::Update(UpdateData::Csv("x,y\n1,2\n3,4".into()));
let table = client.table(data, opts).await?;
let view = table.view(None).await?;
let table2 = client.table(TableData::View(view)).await?;
table.update(data).await?;

Fields

name: String

Implementations

impl View

pub fn new(name: String, client: Client) -> Self

pub async fn column_paths( &self, window: ColumnWindow, ) -> ClientResult<Vec<String>>

Returns an array of strings containing the column paths of the View without any of the source columns.

A column path shows the columns that a given cell belongs to after pivots are applied.

pub async fn dimensions(&self) -> ClientResult<ViewDimensionsResp>

Returns this View’s dimensions, row and column count, as well as those of the crate::Table from which it was derived.

• num_table_rows - The number of rows in the underlying crate::Table.
• num_table_columns - The number of columns in the underlying crate::Table (including the index column if this crate::Table was constructed with one).
• num_view_rows - The number of rows in this View. If this View has a group_by clause, num_view_rows will also include aggregated rows.
• num_view_columns - The number of columns in this View. If this View has a split_by clause, num_view_columns will include all column paths, e.g. the number of columns clause times the number of split_by groups.

pub async fn expression_schema( &self, ) -> ClientResult<HashMap<String, ColumnType>>

The expression schema of this View, which contains only the expressions created on this View. See View::schema for details.

pub async fn get_config(&self) -> ClientResult<ViewConfig>

A copy of the [ViewConfig] object passed to the Table::view method which created this View.

pub async fn num_rows(&self) -> ClientResult<u32>

The number of aggregated rows in this View. This is affected by the “group_by” configuration parameter supplied to this view’s contructor.

Returns

The number of aggregated rows.

pub async fn schema(&self) -> ClientResult<HashMap<String, ColumnType>>

The schema of this View.

The View schema differs from the schema returned by Table::schema; it may have different column names due to expressions or columns configs, or it maye have different column types due to the application og group_by and aggregates config. You can think of Table::schema as the input schema and View::schema as the output schema of a Perspective pipeline.

pub async fn to_arrow(&self, window: ViewWindow) -> ClientResult<Bytes>

Serializes a View to the Apache Arrow data format.

pub async fn to_columns_string( &self, window: ViewWindow, ) -> ClientResult<String>

Serializes this View to a string of JSON data. Useful if you want to save additional round trip serialize/deserialize cycles.

pub async fn to_json_string(&self, window: ViewWindow) -> ClientResult<String>

Render this View as a JSON string.

pub async fn to_ndjson(&self, window: ViewWindow) -> ClientResult<String>

Renders this View as an NDJSON formatted String.

pub async fn to_csv(&self, window: ViewWindow) -> ClientResult<String>

Serializes this View to CSV data in a standard format.

pub async fn delete(&self) -> ClientResult<()>

Delete this View and clean up all resources associated with it. View objects do not stop consuming resources or processing updates when they are garbage collected - you must call this method to reclaim these.

pub async fn get_min_max( &self, column_name: String, ) -> ClientResult<(String, String)>

Calculates the [min, max] of the leaf nodes of a column column_name.

Returns

A tuple of [min, max], whose types are column and aggregate dependent.

pub async fn on_update<T, U>( &self, on_update: T, options: OnUpdateOptions, ) -> ClientResult<u32>

where T: Fn(OnUpdateData) -> U + Send + Sync + 'static, U: Future<Output = ()> + Send + 'static,

Register a callback with this View. Whenever the view’s underlying table emits an update, this callback will be invoked with an object containing port_id, indicating which port the update fired on, and optionally delta, which is the new data that was updated for each cell or each row.

Arguments

• on_update - A callback function invoked on update, which receives an object with two keys: port_id, indicating which port the update was triggered on, and delta, whose value is dependent on the mode parameter.
• options - If this is provided as OnUpdateOptions { mode: Some(OnUpdateMode::Row) }, then delta is an Arrow of the updated rows. Otherwise delta will be Option::None.

pub async fn remove_update(&self, update_id: u32) -> ClientResult<()>

Unregister a previously registered update callback with this View.

Arguments

• id - A callback id as returned by a recipricol call to View::on_update.

Examples

let callback = |_| async { print!("Updated!") };
let cid = view.on_update(callback, OnUpdateOptions::default()).await?;
view.remove_update(cid).await?;

pub async fn on_delete( &self, on_delete: Box<dyn Fn() + Send + Sync + 'static>, ) -> ClientResult<u32>

Register a callback with this View. Whenever the View is deleted, this callback will be invoked.

pub async fn remove_delete(&self, callback_id: u32) -> ClientResult<()>

Unregister a previously registered View::on_delete callback.

pub async fn collapse(&self, row_index: u32) -> ClientResult<u32>

Collapses the group_by row at row_index.

pub async fn expand(&self, row_index: u32) -> ClientResult<u32>

Expand the group_by row at row_index.

pub async fn set_depth(&self, depth: u32) -> ClientResult<()>

Set expansion depth of the group_by tree.

Trait Implementations

impl Clone for View

fn clone(&self) -> View

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for View

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.