(之前的一个问题 Recursively (?) compose LINQ predicates into a single predicate 与此类似,但实际上我问错了问题......那里的解决方案满足了所提出的问题,但实际上并不是我需要的。不过它们是不同的。诚实。)
给定以下搜索文本:
"keyword1 keyword2 ... keywordN"
我想以以下 SQL 结束:
SELECT [columns] FROM Customer
WHERE (
Customer.Forenames LIKE '%keyword1%'
OR
Customer.Forenames LIKE '%keyword2%'
OR
...
OR
Customer.Forenames LIKE '%keywordN%'
) AND (
Customer.Surname LIKE '%keyword1%'
OR
Customer.Surname LIKE '%keyword2%'
OR
....
OR
Customer.Surname LIKE '%keywordN%'
)
实际上,我们在空格上拆分搜索文本,修剪每个标记,基于每个构建一个多部分 OR 子句,然后将这些子句连接在一起。
我在 Linq-to-SQL 中执行此操作,但我不知道如何根据任意长的子谓词列表动态组合谓词。对于已知数量的子句,很容易手动组合谓词:
dataContext.Customers.Where(
(
Customer.Forenames.Contains("keyword1")
||
Customer.Forenames.Contains("keyword2")
) && (
Customer.Surname.Contains("keyword1")
||
Customer.Surname.Contains("keyword2")
)
);
简而言之,我需要一种技术,在给定两个谓词的情况下,该技术将返回一个由两个源谓词与提供的运算符组成的单个谓词,但仅限于 Linq-to-SQL 明确支持的运算符。有什么想法吗?
最佳答案
您可以使用 PredicateBuilder
类
IQueryable<Customer> SearchCustomers (params string[] keywords)
{
var predicate = PredicateBuilder.False<Customer>();
foreach (string keyword in keywords)
{
// Note that you *must* declare a variable inside the loop
// otherwise all your lambdas end up referencing whatever
// the value of "keyword" is when they're finally executed.
string temp = keyword;
predicate = predicate.Or (p => p.Forenames.Contains (temp));
}
return dataContext.Customers.Where (predicate);
}
(这实际上是 PredicateBuilder
页面中的示例,我只是根据您的情况对其进行了调整...)
编辑:
实际上我误解了你的问题,我上面的例子只涵盖了解决方案的一部分......下面的方法应该做你想要的:
IQueryable<Customer> SearchCustomers (string[] forenameKeyWords, string[] surnameKeywords)
{
var predicate = PredicateBuilder.True<Customer>();
var forenamePredicate = PredicateBuilder.False<Customer>();
foreach (string keyword in forenameKeyWords)
{
string temp = keyword;
forenamePredicate = forenamePredicate.Or (p => p.Forenames.Contains (temp));
}
predicate = PredicateBuilder.And(forenamePredicate);
var surnamePredicate = PredicateBuilder.False<Customer>();
foreach (string keyword in surnameKeyWords)
{
string temp = keyword;
surnamePredicate = surnamePredicate.Or (p => p.Surnames.Contains (temp));
}
predicate = PredicateBuilder.And(surnamePredicate);
return dataContext.Customers.Where(predicate);
}
你可以这样使用它:
var query = SearchCustomers(
new[] { "keyword1", "keyword2" },
new[] { "keyword3", "keyword4" });
foreach (var Customer in query)
{
...
}
关于c# - 将 LINQ-to-SQL 谓词组合成单个谓词,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/3782940/