{"id":13635,"date":"2022-08-04T16:02:15","date_gmt":"2022-08-04T23:02:15","guid":{"rendered":"https:\/\/www.couchbase.com\/blog\/?p=13635"},"modified":"2025-06-13T17:20:44","modified_gmt":"2025-06-14T00:20:44","slug":"from-n1ql-to-javascript-and-back-part-3","status":"publish","type":"post","link":"https:\/\/www.couchbase.com\/blog\/pt\/from-n1ql-to-javascript-and-back-part-3\/","title":{"rendered":"De N1QL para JavaScript e vice-versa - Parte 3: Itera\u00e7\u00e3o sobre documentos e DML"},"content":{"rendered":"

Este blog anterior<\/span><\/a> aborda os conceitos b\u00e1sicos da execu\u00e7\u00e3o de instru\u00e7\u00f5es N1QL dentro de fun\u00e7\u00f5es JavaScript.<\/span><\/p>\n

Passamos agora para...<\/span><\/p>\n

Iteradores\/processamento de valores<\/span><\/h2>\n

At\u00e9 agora, evitamos propositalmente declara\u00e7\u00f5es que retornam dados e que retornam dados da fun\u00e7\u00e3o.<\/span><\/p>\n

\u00c9 aqui que come\u00e7amos a explorar a coleta de dados.<\/span><\/p>\n

O N1QL()<\/em> referenciada diretamente ou por meio da m\u00e1gica do transpilador, retorna um identificador de declara\u00e7\u00e3o. O identificador vem na forma de um objeto JavaScript e tem um iterador associado, por exemplo:<\/span><\/p>\n

\u00a0\u00a0\u00a0\u00a0var q = SELECT * FROM b1;<\/pre>\n
N\u00e3o vou gastar muito tempo descrevendo os iteradores, portanto, aqui est\u00e3o os conceitos b\u00e1sicos:<\/span><\/p>\n
    \n
  • Voc\u00ea pode obter o pr\u00f3ximo valor de um iterador usando a fun\u00e7\u00e3o <\/span>pr\u00f3ximo()<\/span> m\u00e9todo.<\/span><\/li>\n
  • O <\/span>feito<\/span> A propriedade \u00e9 verdadeira se n\u00e3o houver mais documentos a serem obtidos.<\/span><\/li>\n
  • Embora voc\u00ea possa usar a fun\u00e7\u00e3o <\/span>pr\u00f3ximo()<\/span><\/em> e <\/span>feito<\/span><\/em> em um loop while para obter todos os documentos, uma constru\u00e7\u00e3o mais leg\u00edvel \u00e9 o <\/span>para...de<\/span><\/em> loop sobre o pr\u00f3prio identificador da declara\u00e7\u00e3o.<\/span><\/li>\n
  • Nem todos os valores precisam ser recuperados - voc\u00ea pode descartar uma declara\u00e7\u00e3o a qualquer momento chamando a fun\u00e7\u00e3o <\/span>fechar()<\/span><\/em> embora, como veremos mais adiante, voc\u00ea n\u00e3o precise fazer isso.<\/span><\/li>\n<\/ul>\n
    Juntando tudo:<\/span>
    \n\"Basics
    \ne a fun\u00e7\u00e3o correspondente:<\/span><\/p>\n
    CREATE FUNCTION doSelect() LANGUAGE JAVASCRIPT AS \"doSelect\" AT \"udfblog\";<\/pre>\n
    Neste exemplo, uma matriz chamada <\/span>res<\/span><\/em> acumula os documentos que obtemos de <\/span>b1<\/em> <\/span>atrav\u00e9s do iterador <\/span>q<\/span><\/em>e, em seguida, \u00e9 usado para devolv\u00ea-los ao chamador.<\/span><\/p>\n
    Algumas observa\u00e7\u00f5es<\/span><\/h3>\n
    Em termos gerais, provavelmente \u00e9 uma ideia melhor processar os valores de consulta \u00e0 medida que s\u00e3o recebidos no <\/span>para<\/span> em vez de apenas acumul\u00e1-los em uma matriz, pois isso tem implica\u00e7\u00f5es transit\u00f3rias no uso da mem\u00f3ria.<\/span><\/p>\n
    Por outro lado, o retorno de um valor de matriz de uma fun\u00e7\u00e3o permite que uma instru\u00e7\u00e3o selecione a fun\u00e7\u00e3o, por exemplo:<\/span><\/p>\n
    SELECT * FROM doSelect() AS funcDocs;<\/pre>\n
    Isso \u00e9 muito parecido com o que voc\u00ea faria com as fun\u00e7\u00f5es de tabela ou tabelas derivadas de cole\u00e7\u00e3o que voc\u00ea encontrou no mundo relacional.<\/span><\/p>\n
    No mundo N1QL, eles s\u00e3o conhecidos como <\/span>exames de express\u00e3o<\/span><\/i>.<\/span><\/p>\n
    \u00c9 claro que, se tudo o que voc\u00ea deseja que sua fun\u00e7\u00e3o fa\u00e7a \u00e9 retornar alguns documentos de um<\/span> Espa\u00e7o-chave<\/span><\/i> sem nenhuma l\u00f3gica adicional, provavelmente \u00e9 melhor escrever uma fun\u00e7\u00e3o inline.<\/span><\/p>\n
    De volta ao iterador!<\/span><\/h3>\n
    Quando voc\u00ea terminar de processar os valores, o iterador se fechar\u00e1 automaticamente, portanto, n\u00e3o h\u00e1 nada que voc\u00ea precise fazer.<\/span><\/p>\n
    Se o iterador n\u00e3o for drenado, \u00e9 uma boa pr\u00e1tica fech\u00e1-lo, embora isso n\u00e3o seja estritamente necess\u00e1rio, pois ele ser\u00e1 fechado automaticamente quando a fun\u00e7\u00e3o retornar, bem como em outras circunst\u00e2ncias, como veremos mais adiante.<\/span><\/p>\n
    Dentro do <\/span>para ... de<\/em> ...<\/span> \u00e9 perfeitamente v\u00e1lido ter outras instru\u00e7\u00f5es N1QL: alguns aspectos a serem considerados ser\u00e3o descritos em se\u00e7\u00f5es posteriores.<\/span><\/p>\n
    Valores de processamento<\/span><\/h3>\n
    Vamos tentar usar os valores retornados pelo select, em vez de apenas retorn\u00e1-los:<\/span><\/p>\n
    function doSelect() {\r\n\u00a0\u00a0\u00a0\u00a0var q = SELECT * FROM b1 LIMIT 2;\r\n\u00a0\u00a0\u00a0\u00a0var res = [];\r\n\u00a0\u00a0\u00a0\u00a0for (const doc of q) {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0let f1 = doc.f1;\r\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0res.push(f1);\r\n\u00a0\u00a0\u00a0\u00a0}\r\n\u00a0\u00a0\u00a0\u00a0return res;\r\n}<\/pre>\n
    Nada particularmente sofisticado, apenas extrair um campo do documento.<\/span><\/p>\n
    A execu\u00e7\u00e3o dessa fun\u00e7\u00e3o produz:<\/span><\/p>\n
    [\r\n\u00a0\u00a0[\r\n\u00a0\u00a0\u00a0\u00a0null,\r\n\u00a0\u00a0\u00a0\u00a0null\r\n\u00a0\u00a0]\r\n]<\/pre>\n
    O que acontece? Por que ele n\u00e3o retorna? f1<\/em>?<\/span><\/p>\n
    Podemos adivinhar a resposta executando:<\/span><\/p>\n
    SELECT * FROM b1 LIMIT 2<\/pre>\n
    E vendo, na interface do usu\u00e1rio:<\/span><\/p>\n
    [\r\n\u00a0\u00a0{\r\n\u00a0\u00a0\u00a0\u00a0\"b1\": {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\"f1\": 1\r\n\u00a0\u00a0\u00a0\u00a0}\r\n\u00a0\u00a0},\r\n\u00a0\u00a0{\r\n\u00a0\u00a0\u00a0\u00a0\"b1\": {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\"f1\": 2\r\n\u00a0\u00a0\u00a0\u00a0}\r\n\u00a0\u00a0}\r\n]<\/pre>\n
    f1<\/span><\/em> \u00e9 um campo em <\/span>b1<\/span><\/em>e n\u00e3o o documento selecionado!<\/span><\/p>\n
    Qualquer um deles faz o que voc\u00ea deseja:<\/span><\/p>\n
    function doSelect() {\r\n\u00a0\u00a0\u00a0\u00a0var q = SELECT * FROM b1 LIMIT 2;\r\n\u00a0\u00a0\u00a0\u00a0var res = [];\r\n\u00a0\u00a0\u00a0\u00a0for (const doc of q) {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0let f1 = doc.b1.f1;\r\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0res.push(f1);\r\n\u00a0\u00a0\u00a0\u00a0}\r\n\u00a0\u00a0\u00a0\u00a0return res;\r\n}<\/pre>\n
    function doSelect() {\r\n\u00a0\u00a0\u00a0\u00a0var q = SELECT raw b1 FROM b1 LIMIT 2;\r\n\u00a0\u00a0\u00a0\u00a0var res = [];\r\n\u00a0\u00a0\u00a0\u00a0for (const doc of q) {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0let f1 = doc.f1;\r\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0res.push(f1);\r\n\u00a0\u00a0\u00a0\u00a0}\r\n\u00a0\u00a0\u00a0\u00a0return res;\r\n}\r\n\r\nfunction doSelect() {\r\n\u00a0\u00a0\u00a0\u00a0var q = SELECT f1 FROM b1 LIMIT 2;\r\n\u00a0\u00a0\u00a0\u00a0var res = [];\r\n\u00a0\u00a0\u00a0\u00a0for (const doc of q) {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0let f1 = doc.f1;\r\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0res.push(f1);\r\n\u00a0\u00a0\u00a0\u00a0}\r\n\u00a0\u00a0\u00a0\u00a0return res;\r\n}<\/pre>\n
     <\/p>\n
    Declara\u00e7\u00f5es DML<\/span><\/h2>\n
    Considere a seguinte fun\u00e7\u00e3o:<\/span><\/p>\n
    function doCopy() {\r\n\u00a0\u00a0\u00a0\u00a0var q1 = INSERT INTO b1 (KEY UUID(), VALUE v) SELECT b1 AS v FROM b1;\r\n\u00a0\u00a0\u00a0\u00a0var q2 = DELETE FROM b1 WHERE LENGTH(meta().id) = 2;\r\n}<\/pre>\n
    CREATE FUNCTION doCopy() LANGUAGE JAVASCRIPT AS \"doCopy\" AT \"udfblog\"<\/pre>\n
    Essa fun\u00e7\u00e3o cria novos documentos em b1<\/em> copiando-os de documentos existentes e removendo os documentos antigos.<\/span><\/p>\n
    O fato de que <\/span>q1<\/span><\/em> e <\/span>q2<\/span><\/em> s\u00e3o iteradores, mesmo quando as instru\u00e7\u00f5es n\u00e3o retornam valores, n\u00e3o deve ser uma grande surpresa: como veremos mais tarde, as instru\u00e7\u00f5es DML podem retornar valores e, pior ainda, o transpilador nem sempre pode determinar se os valores est\u00e3o sendo retornados ou n\u00e3o, da\u00ed o N1QL()<\/em> sempre retorna um iterador.<\/span><\/p>\n
    A implica\u00e7\u00e3o disso \u00e9 que, uma vez que o N1QL()<\/em> a instru\u00e7\u00e3o N1QL pode muito bem estar sendo executada de forma ass\u00edncrona em segundo plano, deixando a fun\u00e7\u00e3o JavaScript livre para executar outro c\u00f3digo antes de buscar os dados.<\/span><\/p>\n
    O jsevaluator<\/em> elimina qualquer ambiguidade comportamental for\u00e7ando as instru\u00e7\u00f5es que n\u00e3o retornam valores a serem executadas imediatamente e em s\u00e9rie, o que significa que ele aguardar\u00e1 a conclus\u00e3o de cada instru\u00e7\u00e3o DML antes de iniciar a pr\u00f3xima instru\u00e7\u00e3o.<\/span><\/p>\n
    Nenhuma a\u00e7\u00e3o no iterador \u00e9 necess\u00e1ria, nem mesmo fech\u00e1-lo.<\/span><\/p>\n
    Isso \u00e9 consistente com o comportamento que esperamos instintivamente: queremos terminar de inserir uma c\u00f3pia dos documentos existentes antes de come\u00e7ar a excluir os antigos - ou talvez n\u00e3o estejamos fazendo uma c\u00f3pia de todos os documentos originais!<\/span><\/p>\n
    Declara\u00e7\u00f5es DML que retornam valores<\/span><\/h2>\n
    Os comandos DML do N1QL podem ser feitos para retornar valores, como na fun\u00e7\u00e3o abaixo:<\/span><\/p>\n
    function doCopy() {\r\n\u00a0\u00a0\u00a0\u00a0var q1 = INSERT INTO b1 (KEY UUID(), VALUE v) SELECT b1 AS v FROM b1 RETURNING meta().id, b1;\r\n\u00a0\u00a0\u00a0\u00a0var res = []\r\n\u00a0\u00a0\u00a0\u00a0for (const doc of q1) {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0res.push(doc);\r\n\u00a0\u00a0\u00a0\u00a0}\r\n\u00a0\u00a0\u00a0\u00a0var q2 = DELETE FROM b1 WHERE LENGTH(meta().id) = 2;\r\n\u00a0\u00a0\u00a0\u00a0return res;\r\n}<\/pre>\n
    Os resultados retornados s\u00e3o processados da mesma forma que para SELECIONAR<\/em> declara\u00e7\u00f5es.<\/span><\/p>\n
    A principal diferen\u00e7a em rela\u00e7\u00e3o \u00e0s instru\u00e7\u00f5es DML que n\u00e3o retornam resultados \u00e9 que, quando nenhum resultado \u00e9 retornado, todas as altera\u00e7\u00f5es no disco s\u00e3o feitas assim que a instru\u00e7\u00e3o retorna, ao passo que, quando os resultados s\u00e3o retornados, a instru\u00e7\u00e3o progride \u00e0 medida que cada documento individual \u00e9 coletado do iterador: voc\u00ea precisa processar todos os valores retornados para que todas as altera\u00e7\u00f5es sejam feitas no disco.<\/span><\/p>\n
    Mais uma vez, a instru\u00e7\u00e3o \u00e9 executada de forma ass\u00edncrona; portanto, ao coletar cada resultado individual, voc\u00ea n\u00e3o deve presumir que essa \u00e9 a \u00faltima modifica\u00e7\u00e3o feita no disco: outras podem j\u00e1 ter sido feitas, com os resultados relevantes apenas na fila esperando para serem coletados.<\/span><\/p>\n
    Assim como as instru\u00e7\u00f5es DML que n\u00e3o retornam resultados, as que retornam s\u00e3o executadas em s\u00e9rie, o que significa que, se voc\u00ea n\u00e3o processar todos os resultados enfileirados no iterador at\u00e9 o momento em que iniciar a pr\u00f3xima instru\u00e7\u00e3o, o jsevaluator concluir\u00e1 a instru\u00e7\u00e3o atual descartando todos os valores n\u00e3o processados.<\/span><\/p>\n
    Conclus\u00e3o<\/span><\/h2>\n
    Cobrimos o processamento de documentos por meio do N1QL e a execu\u00e7\u00e3o da manipula\u00e7\u00e3o de dados.<\/span><\/p>\n
    Em seguida, veremos como lidar com erros.<\/strong><\/p>","protected":false},"excerpt":{"rendered":"
    This earlier blog goes through the basics of executing N1QL statements inside JavaScript functions. We now move onto\u2026 Iterators\/Processing values So far we have purposely avoided statements that return data, and returning data from the function. This is where we […]<\/p>","protected":false},"author":1782,"featured_media":13637,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"categories":[1816,9327,1812],"tags":[2133,1543,8911],"ppma_author":[8924],"class_list":["post-13635","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-couchbase-server","category-javascript","category-n1ql-query","tag-functions","tag-javascript","tag-udf"],"acf":[],"yoast_head":"\nFrom N1QL to JavaScript and Back - Part 3: Iterating over Documents and DML - The Couchbase Blog<\/title>\n<meta name=\"description\" content=\"Learn the basics of iterators in N1QL\/Javascript and Couchbase, the corresponding function, processing documents through N1QL and executing data manipulation.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.couchbase.com\/blog\/pt\/from-n1ql-to-javascript-and-back-part-3\/\" \/>\n<meta property=\"og:locale\" content=\"pt_BR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"From N1QL to JavaScript and Back - 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