Linq To Sql Foreach 循环中的多个Where 搜索

发布于 2024-12-02 14:44:11 字数 813 浏览 2 评论 0原文

我正在尝试使用 where 子句过滤表。当我单独编写查询时，它们工作得很好：

IQueryable<Movie> movies = db.Movies;
movies = movies.Where(movie =>
    movie.MovieToGenres.Any(genreItem => genreItem.Genre_ID == 34)
);
movies = movies.Where(movie =>
    movie.MovieToGenres.Any(genreItem => genreItem.Genre_ID == 35)
);

但是我必须在 foreach 循环中使用它：

List<int> genre_ids = new List<int>();
genre_ids.Add(34);
genre_ids.Add(35);

IQueryable<Movie> movies = db.Movies;
foreach (var genre_id in genre_ids)
{
   movies = movies.Where(movie =>
       movie.MovieToGenres.Any(genreItem => genreItem.Genre_ID == genre_id)
   );
}

当我这样做时，在 SQL 端，查询参数为 @p0 = 35< /code>、@p1 = 35 而不是 @p0 = 34、@p1 = 35。我不知道为什么。

原文

I'm trying to filter a table using where clause. When I the write the queries separately they work fine:

IQueryable<Movie> movies = db.Movies;
movies = movies.Where(movie =>
    movie.MovieToGenres.Any(genreItem => genreItem.Genre_ID == 34)
);
movies = movies.Where(movie =>
    movie.MovieToGenres.Any(genreItem => genreItem.Genre_ID == 35)
);

However I have to use it in a foreach loop:

List<int> genre_ids = new List<int>();
genre_ids.Add(34);
genre_ids.Add(35);

IQueryable<Movie> movies = db.Movies;
foreach (var genre_id in genre_ids)
{
   movies = movies.Where(movie =>
       movie.MovieToGenres.Any(genreItem => genreItem.Genre_ID == genre_id)
   );
}

When I do that, on the SQL side the query parameters are @p0 = 35, @p1 = 35 instead of @p0 = 34, @p1 = 35. I don't know why.

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愁杀 2024-12-09 14:44:11

这是捕获循环变量。所有 lambda 表达式都会捕获一个 genre_id 变量。通过在每次迭代中引入一个新变量并捕获该变量来修复很容易：

foreach (var genre_id in genre_ids)
{
   int genreCopy = genre_id;
   movies = movies.Where(movie => movie.MovieToGenres.Any(
                  genreItem => genreItem.Genre_ID == genreCopy));
}

在 C# 5 中，这可能是不必要的 - 行为很可能正在改变。

It's another case of capturing the loop variable. There's only one genre_id variable which is captured by all the lambda expressions. It's easy to fix by introducing a new variable on each iteration, and capture that instead:

foreach (var genre_id in genre_ids)
{
   int genreCopy = genre_id;
   movies = movies.Where(movie => movie.MovieToGenres.Any(
                  genreItem => genreItem.Genre_ID == genreCopy));
}

In C# 5 this may be unnecessary - the behaviour may well be changing.

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无可置疑 2024-12-09 14:44:11

也许您正在寻找类似的内容，

List<int> genres = new List<int>() { 34, 35, 36 };
movies = movies.Where(movie => movie.MovieToGenres.Any(genreItem => genres.Contains(genreItem.Genre_ID));

它应该翻译为 IN ( 34, 35, 36)

Probably you are looking something like this

List<int> genres = new List<int>() { 34, 35, 36 };
movies = movies.Where(movie => movie.MovieToGenres.Any(genreItem => genres.Contains(genreItem.Genre_ID));

it should translates to IN ( 34, 35, 36)

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