寻找有关如何使用EF解决以下选择查询的建议。
*注意,我仅需要通过EF进行选择的帮助,创建表/插入内容就在其中,仅用于我的表结构示例
CREATE TABLE SampleTable(Foo INT, Bar VARCHAR(50))
INSERT SampleTable VALUES
(1,'GoodData'),
(2, 'BetterData'),
(2, 'Whatever'),
(10, 'GoodData')
SELECT
*
FROM
SampleTable st
WHERE
(Foo = 2 AND Bar = 'BetterData')
OR (Foo = 1 AND Bar = 'GoodData') --There could be a 1000 of these line 'OR' lines
DROP TABLE SampleTable
这里有一些扩展方法可以帮助您:
public static class PredicateBuilder
{
public static Expression<Func<T, bool>> True<T>() { return f => true; }
public static Expression<Func<T, bool>> False<T>() { return f => false; }
public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1,
Expression<Func<T, bool>> expr2)
{
var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
return Expression.Lambda<Func<T, bool>>
(Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);
}
public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1,
Expression<Func<T, bool>> expr2)
{
var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
return Expression.Lambda<Func<T, bool>>
(Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);
}
}
然后将其用于您的动态查询需求:
Expression<Func<SampleTableObject, bool>> predicate = PredicateBuilder.True<SampleTableObject>();
foreach(var item in conditionsList)
{
predicate = predicate.Or(x=>x.Foo == item.Foo && x.Bar == item.Bar);
}
var data = EFContext.SampleTableObjects.Where(predicate);
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我来说两句