Dynamically Build Linq Lambda Expression

Question

Okay, my guess is this is answered somewhere already, and I\'m just not quite familiar enough with the syntax yet to understand, so bear with me.

The users of my web

Answer 1

You could certainly build the expression dynamically, but I would consider using Dynamic LINQ as an alternative first, though you may not be able to use Contains. In addition, you may want to consider using PredicateBuilder to build complex queries additively.

Answer 2

try this code...

call ToExpression Method()....

public static Expression<Func<T, bool>> ToExpression<T>(string andOrOperator, string propName, string opr, string value, Expression<Func<T, bool>> expr = null)
    {
        Expression<Func<T, bool>> func = null;
        try
        {
            ParameterExpression paramExpr = Expression.Parameter(typeof(T));
            var arrProp = propName.Split('.').ToList();
            Expression binExpr = null;
            string partName = string.Empty;
            arrProp.ForEach(x =>
            {
                Expression tempExpr = null;
                partName = partName.IsNull() ? x : partName + "." + x;
                if (partName == propName)
                {
                    var member = NestedExprProp(paramExpr, partName);
                    var type = member.Type.Name == "Nullable`1" ? Nullable.GetUnderlyingType(member.Type) : member.Type;
                    tempExpr = ApplyFilter(opr, member, Expression.Convert(ToExprConstant(type, value), member.Type));
                }
                else
                    tempExpr = ApplyFilter("!=", NestedExprProp(paramExpr, partName), Expression.Constant(null));
                if (binExpr != null)
                    binExpr = Expression.AndAlso(binExpr, tempExpr);
                else
                    binExpr = tempExpr;
            });
            Expression<Func<T, bool>> innerExpr = Expression.Lambda<Func<T, bool>>(binExpr, paramExpr);
            if (expr != null)
                innerExpr = (andOrOperator.IsNull() || andOrOperator == "And" || andOrOperator == "AND" || andOrOperator == "&&") ? innerExpr.And(expr) : innerExpr.Or(expr);
            func = innerExpr;
        }
        catch { }
        return func;
    }

    private static MemberExpression NestedExprProp(Expression expr, string propName)
    {
        string[] arrProp = propName.Split('.');
        int arrPropCount = arrProp.Length;
        return (arrPropCount > 1) ? Expression.Property(NestedExprProp(expr, arrProp.Take(arrPropCount - 1).Aggregate((a, i) => a + "." + i)), arrProp[arrPropCount - 1]) : Expression.Property(expr, propName);
    }

    private static Expression ToExprConstant(Type prop, string value)
    {
        if (value.IsNull())
            return Expression.Constant(value);
        object val = null;
        switch (prop.FullName)
        {
            case "System.Guid":
                val = value.ToGuid();
                break;
            default:
                val = Convert.ChangeType(value, Type.GetType(prop.FullName));
                break;
        }
        return Expression.Constant(val);
    }

    private static Expression ApplyFilter(string opr, Expression left, Expression right)
    {
        Expression InnerLambda = null;
        switch (opr)
        {
            case "==":
            case "=":
                InnerLambda = Expression.Equal(left, right);
                break;
            case "<":
                InnerLambda = Expression.LessThan(left, right);
                break;
            case ">":
                InnerLambda = Expression.GreaterThan(left, right);
                break;
            case ">=":
                InnerLambda = Expression.GreaterThanOrEqual(left, right);
                break;
            case "<=":
                InnerLambda = Expression.LessThanOrEqual(left, right);
                break;
            case "!=":
                InnerLambda = Expression.NotEqual(left, right);
                break;
            case "&&":
                InnerLambda = Expression.And(left, right);
                break;
            case "||":
                InnerLambda = Expression.Or(left, right);
                break;
            case "LIKE":
                InnerLambda = Expression.Call(left, typeof(string).GetMethod("Contains", new Type[] { typeof(string) }), right);
                break;
            case "NOTLIKE":
                InnerLambda = Expression.Not(Expression.Call(left, typeof(string).GetMethod("Contains", new Type[] { typeof(string) }), right));
                break;
        }
        return InnerLambda;
    }

    public static Expression<Func<T, object>> PropExpr<T>(string PropName)
    {
        ParameterExpression paramExpr = Expression.Parameter(typeof(T));
        var tempExpr = Extentions.NestedExprProp(paramExpr, PropName);
        return Expression.Lambda<Func<T, object>>(Expression.Convert(Expression.Lambda(tempExpr, paramExpr).Body, typeof(object)), paramExpr);

    }
    public static IQueryOver<T, T> OrderBy<T>(this IQueryOver<T, T> Collection, string sidx, string sord)
    {
        return sord == "asc" ? Collection.OrderBy(NHibernate.Criterion.Projections.Property(sidx)).Asc : Collection.OrderBy(NHibernate.Criterion.Projections.Property(sidx)).Desc;
    }

    public static Expression<Func<T, TResult>> And<T, TResult>(this Expression<Func<T, TResult>> expr1, Expression<Func<T, TResult>> expr2)
    {
        var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
        return Expression.Lambda<Func<T, TResult>>(Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);
    }

    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);
    }