14-fetch-value-xxx.md

.fetchValueXxx()

• .fetchValueXxx() ignores all previous calls to .map()
• .fetchValueXxx() may only be called if the SELECT clause is of length one and a column or aliased expression is selected.

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The .fetchValueXxx() methods fetch a single row, at most.

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Overview

• .fetchValue()
• .fetchValueOr()
• .fetchValueOrUndefined()

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.fetchValue()

Convenience method for,

const row : { myColumn : bigint } = await tsql
    .from(myTable)
    .select(columns => [columns.myColumn])
    .fetchOne(connection);

const bigintValue : bigint = row.myColumn;

Usage,

const bigintValue : bigint = await tsql
    .from(myTable)
    .select(columns => [columns.myColumn])
    .fetchValue(connection);

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.fetchValueOr(connection, defaultValue)

Convenience method for,

const row : { myColumn : bigint }|string = await tsql
    .from(myTable)
    .select(columns => [columns.myColumn])
    .fetchOneOr(connection, "whoops, no value");

const bigintOrStringValue : bigint|string = (
    typeof row == "string" ?
    row :
    row.myColumn
);

Usage,

const bigintOrStringValue : bigint|string = await tsql
    .from(myTable)
    .select(columns => [columns.myColumn])
    .fetchValueOr(connection, "whoops, no value");

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.fetchValueOrUndefined()

Convenience method for .fetchValueOr(connection, undefined).

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ExecutionUtil.FetchValuePromise<>

.fetchValue() actually returns a value of type ExecutionUtil.FetchValuePromise<>

It is essentially the same as Promise<>, with two extra methods,

• .or(defaultValue)

  Behaves the same as .fetchValueOr()

  myQuery
      .fetchValue(connection)
      .or(1337)
      .then((value) => {
          if (value == 1337) {
              //No value was fetched... Or the value fetched is 1337
          } else {
              //A value was fetched
          }
      });

• .orUndefined()

  Behaves the same as .fetchValueOrUndefined()

  myQuery
      .fetchValue(connection)
      .orUndefined()
      .then((value) => {
          if (value == undefined) {
              //No value was fetched
          } else {
              //A value was fetched
          }
      });