如何在循环中为IQueryable变量添加Where与OR条件

你需要生成包含多个OR条件的SQL查询，但直接使用Where方法会叠加AND逻辑，无法满足需求。以下是两种可行的实现方案：

方案一：使用LinqKit的PredicateBuilder（推荐） #

LinqKit提供的PredicateBuilder可以轻松组合OR/AND条件，需要先通过NuGet安装LinqKit.Microsoft.EntityFrameworkCore包。

代码示例：

using LinqKit;

// 初始化基础查询，包含IsDeleted过滤
var baseQuery = DbContext.EmployeeSearches.AsQueryable();
var predicate = PredicateBuilder.New<EmployeeSearch>(e => !e.IsDeleted);

// 模拟12次迭代的名称匹配逻辑
for (int x = 0; x < 12; x++)
{
    string targetName;
    if (x == 0)
    {
        targetName = fd.Value.ToString() == "None" ? "None" : filter.Value.ToString();
    }
    else
    {
        // 替换为你实际的第x个EmployeeName值
        targetName = $"EmployeeName_{x}";
    }

    // 叠加OR条件：匹配null/None或指定名称
    if (targetName == "None")
    {
        predicate = predicate.Or(e => e.EmployeeName == null || e.EmployeeName == "None");
    }
    else
    {
        predicate = predicate.Or(e => e.EmployeeName == targetName);
    }
}

// 应用组合后的谓词生成最终查询
var result = baseQuery.AsExpandable().Where(predicate);

方案二：手动构建表达式树（无第三方依赖） #

如果不想引入外部包，可以手动通过表达式树组合OR条件：

代码示例：

using System.Linq.Expressions;

// 初始化基础查询
var baseQuery = DbContext.EmployeeSearches.AsQueryable();
Expression<Func<EmployeeSearch, bool>> combinedPredicate = e => !e.IsDeleted;

for (int x = 0; x < 12; x++)
{
    string targetName;
    if (x == 0)
    {
        targetName = fd.Value.ToString() == "None" ? "None" : filter.Value.ToString();
    }
    else
    {
        // 替换为实际的名称值
        targetName = $"EmployeeName_{x}";
    }

    // 创建当前迭代的条件表达式
    Expression<Func<EmployeeSearch, bool>> currentPredicate;
    if (targetName == "None")
    {
        currentPredicate = e => e.EmployeeName == null || e.EmployeeName == "None";
    }
    else
    {
        currentPredicate = e => e.EmployeeName == targetName;
    }

    // 组合现有表达式与当前表达式（OR逻辑）
    var parameter = Expression.Parameter(typeof(EmployeeSearch));
    var combinedBody = Expression.OrElse(
        Expression.Invoke(combinedPredicate, parameter),
        Expression.Invoke(currentPredicate, parameter)
    );
    combinedPredicate = Expression.Lambda<Func<EmployeeSearch, bool>>(combinedBody, parameter);
}

// 应用最终条件
var result = baseQuery.Where(combinedPredicate);

两种方案最终生成的SQL都会符合你期望的格式：

Select * from Employee Where IsDeleted = 0 AND (EmployeeName = 'None' OR EmployeeName='John' OR EmployeeName='Lucy')

内容的提问来源于stack exchange，提问作者Alevel