from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Union[str, None] = Query(
        default=None, min_length=3, max_length=50, pattern="^fixedquery$"
    ),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})

    assertThat(ArbitraryInstances.get(GenericDeclaration.class)).isNotNull();
  }

  public void testGet_regex() {
    assertEquals(Pattern.compile("").pattern(), ArbitraryInstances.get(Pattern.class).pattern());
    assertEquals(0, ArbitraryInstances.get(MatchResult.class).groupCount());
  }

  public void testGet_usePublicConstant() {

Ahora sabes que cuando las necesites puedes usarlas en **FastAPI**.

### Pydantic v1 `regex` en lugar de `pattern` { #pydantic-v1-regex-instead-of-pattern }

Antes de la versión 2 de Pydantic y antes de FastAPI 0.100.0, el parámetro se llamaba `regex` en lugar de `pattern`, pero ahora está en desuso.

Todavía podrías ver algo de código que lo usa:

//// tab | Pydantic v1

          .put(BigInteger.class, BigInteger.ZERO)
          .put(BigDecimal.class, BigDecimal.ZERO)
          .put(CharSequence.class, "")
          .put(String.class, "")
          .put(Pattern.class, Pattern.compile(""))
          .put(MatchResult.class, createMatchResult())
          .put(TimeUnit.class, SECONDS)
          .put(Charset.class, UTF_8)
          .put(Currency.class, Currency.getInstance(Locale.US))

Але тепер Ви знаєте, що коли вони знадобляться, їх можна застосовувати у **FastAPI**.

### Pydantic v1 `regex` замість `pattern`

До версії Pydantic 2 і FastAPI 0.100.0 параметр називався `regex` замість `pattern`, але тепер він застарів.

Ви все ще можете зустріти код, який використовує його:

//// tab | Pydantic v1

    assertThat(ArbitraryInstances.get(GenericDeclaration.class)).isNotNull();
  }

  public void testGet_regex() {
    assertEquals(Pattern.compile("").pattern(), ArbitraryInstances.get(Pattern.class).pattern());
    assertEquals(0, ArbitraryInstances.get(MatchResult.class).groupCount());
  }

  public void testGet_usePublicConstant() {

You can define a <abbr title="A regular expression, regex or regexp is a sequence of characters that define a search pattern for strings.">regular expression</abbr> `pattern` that the parameter should match:

{* ../../docs_src/query_params_str_validations/tutorial004_an_py310.py hl[11] *}

This specific regular expression pattern checks that the received parameter value:

* `^`: starts with the following characters, doesn't have characters before.

	rulesCase7.Add(NewPattern("", "*.jpg"), TargetID{"1", "webhook"})

	rulesCase8 := make(Rules)
	rulesCase8.Add(NewPattern("2010*", ""), TargetID{"1", "webhook"})

	testCases := []struct {
		rules          Rules
		pattern        string
		targetID       TargetID
		expectedResult int
	}{
		{rulesCase1, NewPattern("*", ""), TargetID{"1", "webhook"}, 1},
		{rulesCase2, NewPattern("*", ""), TargetID{"2", "amqp"}, 2},

	}, "*", TargetID{"1", "webhook"})

	rulesMapCase3 := make(RulesMap)
	rulesMapCase3.add([]Name{ObjectRemovedDelete}, "2010*.jpg", TargetID{"1", "webhook"})

	testCases := []struct {
		eventNames     []Name
		pattern        string
		targetID       TargetID
		expectedResult RulesMap
	}{
		{[]Name{ObjectAccessedAll}, "", TargetID{"1", "webhook"}, rulesMapCase1},

    return string || "";
  }-*/;

  @JsMethod
  static native String emptyToNull(@Nullable String string) /*-{
    return string || null;
  }-*/;

  static CommonPattern compilePattern(String pattern) {
    throw new UnsupportedOperationException();
  }

  static boolean patternCompilerIsPcreLike() {
    throw new UnsupportedOperationException();
  }