Linq to Entity 动态拼接查询条件(重点是OR)

/// <summary>
/// linq动态条件
/// 构造函数使用True时：单个AND有效，多个AND有效；单个OR无效，多个OR无效；混合时写在AND后的OR有效
/// 构造函数使用False时：单个AND无效，多个AND无效；单个OR有效，多个OR有效；混合时写在OR后面的AND有效
/// </summary>
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);
}
}

2.使用(只是例子)

var predicate = Lib.Linq.PredicateBuilder.False<CompanyExpansionInfo>();
foreach (var item in input.ChooseMaterials)
{
string str = item.ToString();
predicate = predicate.Or(t => t.ManufacturingMaterials.Contains(str));
}

expansionlist = expansionlist.Where(predicate);

如果以上不懂，可尝试使用以下方法

namespace Lib
{
    /// <summary>
    /// 合并表达式 And Or  Not扩展
    /// </summary>
    public static class ExpressionExtend
    {
        /// <summary>
        /// 合并表达式 expr1 AND expr2
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="expr1"></param>
        /// <param name="expr2"></param>
        /// <returns></returns>
        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
        {
            if (expr1 == null)
                return expr2;
            else if (expr2 == null)
                return expr1;            
            ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
            NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);
            var left = visitor.Replace(expr1.Body);
            var right = visitor.Replace(expr2.Body);
            var body = Expression.And(left, right);
            return Expression.Lambda<Func<T, bool>>(body, newParameter);
        }
        /// <summary>
        /// 合并表达式 expr1 or expr2
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="expr1"></param>
        /// <param name="expr2"></param>
        /// <returns></returns>
        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
        {
            if (expr1 == null)
                return expr2;
            else if (expr2 == null)
                return expr1;
            ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
            NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);
            var left = visitor.Replace(expr1.Body);
            var right = visitor.Replace(expr2.Body);
            var body = Expression.Or(left, right);
            return Expression.Lambda<Func<T, bool>>(body, newParameter);
        }
        public static Expression<Func<T, bool>> Not<T>(this Expression<Func<T, bool>> expr)
        {
            if (expr == null)
                return null;
            var candidateExpr = expr.Parameters[0];
            var body = Expression.Not(expr.Body);
            return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
        }
    }
    /// <summary>
    /// 建立新表达式
    /// </summary>
    internal class NewExpressionVisitor : ExpressionVisitor
    {
        public ParameterExpression _NewParameter { get; private set; }
        public NewExpressionVisitor(ParameterExpression param)
        {
            this._NewParameter = param;
        }
        public Expression Replace(Expression exp)
        {
            return this.Visit(exp);
        }
        protected override Expression VisitParameter(ParameterExpression node)
        {
            return this._NewParameter;
        }
    }
}
//实例：
//Expression<Func<People, bool>> lambda1 = x => x.Age > 5;
//Expression<Func<People, bool>> lambda2 = x => x.Id > 5;
//Expression<Func<People, bool>> lambda3 = lambda1.And(lambda2);
//Expression<Func<People, bool>> lambda4 = lambda1.Or(lambda2);
//Expression<Func<People, bool>> lambda5 = lambda1.Not();