Add __table function and unit tests

package.json

@@ -22,6 +22,7 @@
     "dist/**/*.js"
   ],
   "dependencies": {
+    "d3-array": "^3.2.0",
     "d3-dsv": "^2.0.0",
     "d3-require": "^1.3.0"
   },

src/index.mjs

@@ -1,3 +1,3 @@
 export {default as FileAttachments, AbstractFile} from "./fileAttachment.mjs";
 export {default as Library} from "./library.mjs";
-export {makeQueryTemplate} from "./table.mjs";
+export {makeQueryTemplate, isDataArray, isDatabaseClient} from "./table.mjs";

src/table.mjs

@@ -1,12 +1,153 @@
+import {ascending, descending, reverse} from "d3-array";
+
+const nChecks = 20; // number of values to check in each array
+
+// We support two levels of DatabaseClient. The simplest DatabaseClient
+// implements only the client.sql tagged template literal. More advanced
+// DatabaseClients implement client.query and client.queryStream, which support
+// streaming and abort, and the client.queryTag tagged template literal is used
+// to translate the contents of a SQL cell or Table cell into the appropriate
+// arguments for calling client.query or client.queryStream. For table cells, we
+// additionally require client.describeColumns. The client.describeTables method
+// is optional.
+export function isDatabaseClient(value, mode) {
+  return (
+    value &&
+    (typeof value.sql === "function" ||
+      (typeof value.queryTag === "function" &&
+        (typeof value.query === "function" ||
+          typeof value.queryStream === "function"))) &&
+    (mode !== "table" || typeof value.describeColumns === "function") &&
+    value !== __query // don’t match our internal helper
+  );
+}
+
+// Returns true if the value is a typed array (for a single-column table), or if
+// it’s an array. In the latter case, the elements of the array must be
+// consistently typed: either plain objects or primitives or dates.
+export function isDataArray(value) {
+  return (
+    (Array.isArray(value) &&
+      (isQueryResultSetSchema(value.schema) ||
+        isQueryResultSetColumns(value.columns) ||
+        arrayContainsObjects(value) ||
+        arrayContainsPrimitives(value) ||
+        arrayContainsDates(value))) ||
+    isTypedArray(value)
+  );
+}
+
+// Given an array, checks that the given value is an array that does not contain
+// any primitive values (at least for the first few values that we check), and
+// that the first object contains enumerable keys (see computeSchema for how we
+// infer the columns). We assume that the contents of the table are homogenous,
+// but we don’t currently enforce this.
+// https://observablehq.com/@observablehq/database-client-specification#§1
+function arrayContainsObjects(value) {
+  const n = Math.min(nChecks, value.length);
+  for (let i = 0; i < n; ++i) {
+    const v = value[i];
+    if (v === null || typeof v !== "object") return false;
+  }
+  return n > 0 && objectHasEnumerableKeys(value[0]);
+}
+
+// Using a for-in loop here means that we can abort after finding at least one
+// enumerable key (whereas Object.keys would require materializing the array of
+// all keys, which would be considerably slower if the value has many keys!).
+// This function assumes that value is an object; see arrayContainsObjects.
+function objectHasEnumerableKeys(value) {
+  for (const _ in value) return true;
+  return false;
+}
+
+function isQueryResultSetSchema(schemas) {
+  return (Array.isArray(schemas) && schemas.every((s) => s && typeof s.name === "string"));
+}
+
+function isQueryResultSetColumns(columns) {
+  return (Array.isArray(columns) && columns.every((name) => typeof name === "string"));
+}
+
+// Returns true if the value represents an array of primitives (i.e., a
+// single-column table). This should only be passed values for which
+// canDisplayTable returns true.
+function arrayIsPrimitive(value) {
+  return (
+    isTypedArray(value) ||
+    arrayContainsPrimitives(value) ||
+    arrayContainsDates(value)
+  );
+}
+
+// Given an array, checks that the first n elements are primitives (number,
+// string, boolean, bigint) of a consistent type.
+function arrayContainsPrimitives(value) {
+  const n = Math.min(nChecks, value.length);
+  if (!(n > 0)) return false;
+  let type;
+  let hasPrimitive = false; // ensure we encounter 1+ primitives
+  for (let i = 0; i < n; ++i) {
+    const v = value[i];
+    if (v == null) continue; // ignore null and undefined
+    const t = typeof v;
+    if (type === undefined) {
+      switch (t) {
+        case "number":
+        case "boolean":
+        case "string":
+        case "bigint":
+          type = t;
+          break;
+        default:
+          return false;
+      }
+    } else if (t !== type) {
+      return false;
+    }
+    hasPrimitive = true;
+  }
+  return hasPrimitive;
+}
+
+// Given an array, checks that the first n elements are dates.
+function arrayContainsDates(value) {
+  const n = Math.min(nChecks, value.length);
+  if (!(n > 0)) return false;
+  let hasDate = false; // ensure we encounter 1+ dates
+  for (let i = 0; i < n; ++i) {
+    const v = value[i];
+    if (v == null) continue; // ignore null and undefined
+    if (!(v instanceof Date)) return false;
+    hasDate = true;
+  }
+  return hasDate;
+}
+
+function isTypedArray(value) {
+  return (
+    value instanceof Int8Array ||
+    value instanceof Int16Array ||
+    value instanceof Int32Array ||
+    value instanceof Uint8Array ||
+    value instanceof Uint8ClampedArray ||
+    value instanceof Uint16Array ||
+    value instanceof Uint32Array ||
+    value instanceof Float32Array ||
+    value instanceof Float64Array
+  );
+}
+
+// __query is used by table cells; __query.sql is used by SQL cells.
 export const __query = Object.assign(
-  // This function is used by table cells.
   async (source, operations, invalidation) => {
-    const args = makeQueryTemplate(operations, await source);
-    if (!args) return null; // the empty state
-    return evaluateQuery(await source, args, invalidation);
+    source = await source;
+    if (isDatabaseClient(source)) return evaluateQuery(source, makeQueryTemplate(operations, source), invalidation);
+    if (isDataArray(source)) return __table(source, operations);
+    if (!source) throw new Error("missing data source");
+    throw new Error("invalid data source");
   },
   {
-    // This function is used by SQL cells.
     sql(source, invalidation) {
       return async function () {
         return evaluateQuery(source, arguments, invalidation);
@@ -16,7 +157,7 @@ export const __query = Object.assign(
 );
 
 async function evaluateQuery(source, args, invalidation) {
-  if (!source) return;
+  if (!source) throw new Error("missing data source");
 
   // If this DatabaseClient supports abort and streaming, use that.
   if (typeof source.queryTag === "function") {
@@ -73,17 +214,15 @@ async function* accumulateQuery(queryRequest) {
  * of sub-strings and params are the parameter values to be inserted between each
  * sub-string.
  */
- export function makeQueryTemplate(operations, source) {
+export function makeQueryTemplate(operations, source) {
   const escaper =
-    source && typeof source.escape === "function" ? source.escape : (i) => i;
+    typeof source.escape === "function" ? source.escape : (i) => i;
   const {select, from, filter, sort, slice} = operations;
-  if (
-    from.table === null ||
-    select.columns === null ||
-    (select.columns && select.columns.length === 0)
-  )
-    return;
-  const columns = select.columns.map((c) => `t.${escaper(c)}`);
+  if (!from.table)
+    throw new Error("missing from table");
+  if (select.columns?.length === 0)
+    throw new Error("at least one column must be selected");
+  const columns = select.columns ? select.columns.map((c) => `t.${escaper(c)}`) : "*";
   const args = [
     [`SELECT ${columns} FROM ${formatTable(from.table, escaper)} t`]
   ];
@@ -108,7 +247,7 @@ async function* accumulateQuery(queryRequest) {
 }
 
 function formatTable(table, escaper) {
-  if (typeof table === "object") {
+  if (typeof table === "object") { // i.e., not a bare string specifier
     let from = "";
     if (table.database != null) from += escaper(table.database) + ".";
     if (table.schema != null) from += escaper(table.schema) + ".";
@@ -231,3 +370,113 @@ function likeOperand(operand) {
   return {...operand, value: `%${operand.value}%`};
 }
 
+// This function applies table cell operations to an in-memory table (array of
+// objects); it should be equivalent to the corresponding SQL query.
+export function __table(source, operations) {
+  if (arrayIsPrimitive(source)) source = Array.from(source, (value) => ({value}));
+  const input = source;
+  let {schema, columns} = source;
+  for (const {type, operands} of operations.filter) {
+    const [{value: column}] = operands;
+    const values = operands.slice(1).map(({value}) => value);
+    switch (type) {
+      case "eq": {
+        const [value] = values;
+        if (value instanceof Date) {
+          const time = +value; // compare as primitive
+          source = source.filter((d) => +d[column] === time);
+        } else {
+          source = source.filter((d) => d[column] === value);
+        }
+        break;
+      }
+      case "ne": {
+        const [value] = values;
+        source = source.filter((d) => d[column] !== value);
+        break;
+      }
+      case "c": {
+        const [value] = values;
+        source = source.filter(
+          (d) => typeof d[column] === "string" && d[column].includes(value)
+        );
+        break;
+      }
+      case "nc": {
+        const [value] = values;
+        source = source.filter(
+          (d) => typeof d[column] === "string" && !d[column].includes(value)
+        );
+        break;
+      }
+      case "in": {
+        const set = new Set(values); // TODO support dates?
+        source = source.filter((d) => set.has(d[column]));
+        break;
+      }
+      case "nin": {
+        const set = new Set(values); // TODO support dates?
+        source = source.filter((d) => !set.has(d[column]));
+        break;
+      }
+      case "n": {
+        source = source.filter((d) => d[column] == null);
+        break;
+      }
+      case "nn": {
+        source = source.filter((d) => d[column] != null);
+        break;
+      }
+      case "lt": {
+        const [value] = values;
+        source = source.filter((d) => d[column] < value);
+        break;
+      }
+      case "lte": {
+        const [value] = values;
+        source = source.filter((d) => d[column] <= value);
+        break;
+      }
+      case "gt": {
+        const [value] = values;
+        source = source.filter((d) => d[column] > value);
+        break;
+      }
+      case "gte": {
+        const [value] = values;
+        source = source.filter((d) => d[column] >= value);
+        break;
+      }
+      default:
+        throw new Error(`unknown filter type: ${type}`);
+    }
+  }
+  for (const {column, direction} of reverse(operations.sort)) {
+    const compare = direction === "desc" ? descending : ascending;
+    if (source === input) source = source.slice(); // defensive copy
+    source.sort((a, b) => compare(a[column], b[column]));
+  }
+  let {from, to} = operations.slice;
+  from = from == null ? 0 : Math.max(0, from);
+  to = to == null ? Infinity : Math.max(0, to);
+  if (from > 0 || to < Infinity) {
+    source = source.slice(Math.max(0, from), Math.max(0, to));
+  }
+  if (operations.select.columns) {
+    if (schema) {
+      const schemaByName = new Map(schema.map((s) => [s.name, s]));
+      schema = operations.select.columns.map((c) => schemaByName.get(c));
+    }
+    if (columns) {
+      columns = operations.select.columns;
+    }
+    source = source.map((d) =>
+      Object.fromEntries(operations.select.columns.map((c) => [c, d[c]]))
+    );
+  }
+  if (source !== input) {
+    if (schema) source.schema = schema;
+    if (columns) source.columns = columns;
+  }
+  return source;
+}