在ecto中结合两个where查询

Question

我正在尝试创建一个 ecto 查询，当两个查询都满足时返回结果。当我运行应用程序时，我收到错误 function nil.title/0 is undefined or private。这是因为我没有正确的查询吗？我想要一个 AND 在两个 where 上。

def next_prod do
  Post |> where(postStatus: "published") |> where(next_prod: "yes") |> Repo.one()
end

SQL 查询

您会看到有一条记录应该与 ecto 查询匹配。

iex(1)> Codsonline.Repo.query("SELECT * FROM posts")
[debug] QUERY OK db=3.0ms queue=0.1ms
SELECT * FROM posts []
{:ok,
 %Postgrex.Result{columns: ["id", "title", "snippet", "body", "slug", "mainImg",
   "thumbImg", "postStatus", "showStatus", "inserted_at", "updated_at",
   "next_prod"], command: :select, connection_id: 13732, num_rows: 1,
  rows: [[8, "Blackadder Goes Forth",
    "“Blackadder Goes Forth ” is the fourth and final part of the Blackadder series . A theatrical Dramatisation inspired by the TV episodes. Follow the Wit and Sarcasm of Captain BlackAdder  in Oscar Wilde language.",
    "27th January – 03rd February 2018\r\nPlayhouse Theatre, Cheltenham\r\n\r\n \r\n\r\nEpisodes:\r\n‘Corporal Punishment‘ (Episode 2)\r\n‘Private Plane‘ (Episode 4)\r\n‘Goodbyeee‘ (Episode 6)\r\n\r\nDirected by Nick Tobias & Liz White\r\n\r\n \r\n\r\nCast List:\r\n\r\nCaptain Edmund Blackadder – Chris Hannant\r\nPrivate S Baldrick – Matt Wilson\r\nLt. Hon. George Colthurst St Barleigh – UNCAST\r\nGeneral Sir Anthony Cecil Hogmanay Melchett – Jason Blackburn\r\nCaptain Kevin Darling – Jack Homer\r\nSquadron Commander the Lord Flashheart – Michael Fay\r\nField Marshall Sir Douglas Haig – Will Browne\r\nBaron Von Richthoven – Robert Barton-Ancliffe\r\nBob ‘Bobbie’ Parkhurst – Sarah Bottomley\r\n\r\nEnsemble – Ben Wilson (Sergeant Jones), Oliver Chapman (Gerhardt), Michael Sheldrick (Perkins), Steve Scott, Matthew Morris",
    "blackadder-goes-forth", ".", ".", "published", "Future",
    {{2017, 11, 18}, {22, 36, 19, 408441}},
    {{2017, 11, 18}, {23, 3, 42, 816258}}, "Yes"]]}}

Answer 1

该错误不是来自这行代码。您的代码很好，这两个子句将由 Ecto 进行“与”运算。该错误表示您试图在某处调用nil.title。

iex(1)> nil.title
** (UndefinedFunctionError) function nil.title/0 is undefined or private
    nil.title()

我猜你在这个函数的返回值上调用了.title，而你实际上在数据库中没有匹配这两个条件的记录。如果您想确保记录存在，您应该使用Repo.one!。或者如果你想处理记录不存在的情况，使用if：

if record = Thing.next_prod do
  # record exists
else
  # it doesn't
end