[英]combine predicates into expression
我旨在使用此簽名:
IEnumerable<T> SearchFor(Expression<Func<T, bool>> expression);
並希望將這兩個謂詞與:
Func<Employee, bool> isActiveEmployee = e => e.DateFired == null;
Func<Employee, bool> isNewEmployee = e => e.DateHired >= DateTime.Today.AddDays(-90);
成為表達。 請問我該如何實現?
PS:
基本上,我正在嘗試使用this 。 但是這行:
var body = (BinaryExpression) expression.Body;
從此處獲取的方法GetDynamicQuery
中拋出異常:
無法將類型為“ System.Linq.Expressions.InstanceMethodCallExpressionN”的對象轉換為類型為“ System.Linq.Expressions.BinaryExpression”的對象。
使用這種方法:
Expression<Func<Employee, bool>> isActiveEmployee = e => e.DateFired == null;
Expression<Func<Employee, bool>> isNewEmployee = e => e.DateHired >= DateTime.Today.AddDays(-90);
Expression<Func<Employee, bool>> combined_expression = e => isActiveEmployee.Invoke(e) && isNewEmployee.Invoke(e);
我假設您需要一個可以由許多數據訪問框架轉換為SQL的真實表達式。
一種解決方案是像這樣使用LinqKit :
Expression<Func<Employee, bool>> isActiveEmployee = e => e.DateFired == null;
Expression<Func<Employee, bool>> isNewEmployee = e => e.DateHired >= DateTime.Today.AddDays(-90);
Expression<Func<Employee, bool>> combined_expression = e => isActiveEmployee.Invoke(e) && isNewEmployee.Invoke(e);
然后,您可以使用AsExpandable
方法包裝IQueryable
,如下所示:
var query = context.Employees.AsExpandable().Where(combined_expression);
或者,如果您不想調用AsExpandable
,則可以展開新表達式,然后像其他任何表達式一樣使用它:
Expression<Func<Employee, bool>> combined_expression = e => isActiveEmployee.Invoke(e) && isNewEmployee.Invoke(e);
combined_expression = combined_expression.Expand();
var query = context.Employees.Where(combined_expression);
更新:
對於您提供的第二個示例,可以執行以下操作:
Expression<Func<Employee, bool>> expression1 = e => e.Guid == new Guid("28D3BCFB-9472-4141-BD88-BE5E7E1230F0");
Expression<Func<Employee, bool>> expression2 = e => e.Guid == new Guid("0F0DBA45-F842-4E46-9ED4-F50B5BCF0509");
Expression<Func<Employee, bool>> combined_expression = e => expression1.Invoke(e) || expression2.Invoke(e);
combined_expression = combined_expression.Expand();
// use combined_expression
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