Develop Reference

Return false if type properties equals null or 0

I tried following the method as follows here: Checking if Object has null in every property . However, when instantiating Order newOrder = new Order();. I cannot simple just implement bool props = newOrder.ArePropertiesNotNull(). What am I supposed to add to my Order class? And where do I implement the function for ArePropertiesNotNull<T>(this T obj)? I would like to know if there is a way to return false if value returned equals 0 or null?
Here is my code:
OrderProdRepository.cs
...
public bool ReadFromFile(string _date)
{
taxesFile.ReadFile();
productsFile.ReadFile();
string orderFileName = $"C:\\tempfolder\\Orders_{_date}.txt";
List<string> lines = File.ReadAllLines(orderFileName).ToList();
foreach (var line in lines.Skip(1)) //?? new List<string>(0)
{
List<string> entry = line.Split(',').ToList();
Order newOrder = new Order();
int.TryParse(entry[0], out int orderNumber);
newOrder.OrderNumber = orderNumber;
newOrder.Date = _date;
newOrder.CustomerName = entry[1];
newOrder.State = taxesFile.StateAbbreviation(entry[2]);
newOrder.StateName = taxesFile.StateName(newOrder.State);
decimal.TryParse(entry[3], out decimal taxRate);
newOrder.TaxRate = taxesFile.TaxRate(taxRate);
newOrder.ProductType = productsFile.ProductType(entry[4]);
decimal.TryParse(entry[5], out decimal area);
newOrder.Area = area;
decimal.TryParse(entry[6], out decimal costPerSquareFoot);
newOrder.CostPerSquareFoot = productsFile.CostPerSquareFoot(costPerSquareFoot);
decimal.TryParse(entry[7], out decimal laborCostPerSquareFoot);
newOrder.LaborCostPerSquareFoot = productsFile.LaborCostPerSquareFoot(laborCostPerSquareFoot);
decimal.TryParse(entry[8], out decimal materialCost);
newOrder.MaterialCost = materialCost;
decimal.TryParse(entry[9], out decimal laborCost);
newOrder.LaborCost = laborCost;
decimal.TryParse(entry[10], out decimal tax);
newOrder.Tax = tax;
decimal.TryParse(entry[11], out decimal total);
newOrder.Total = total;
orderList.Add(newOrder);
}
return true;
}
...

I think you need a function to check each line for null and/or 0 values:
private bool IsValidLine(string line)
{
if (line == null)
return false;
var arr = line.Split(',');
//Uncomment this if splitting the line will always return 11 items array.
//if (arr.Length < 11)
// return false;
return arr.Aggregate(0, (n, s) =>
(decimal.TryParse(s, out decimal d) && d == 0) ||
string.IsNullOrWhiteSpace(s) ? n + 1 : n) == 0;
}
You can use it in your code as follows:
public bool ReadFromFile(string _date)
{
var orderFileName = $"C:\\tempfolder\\Orders_{_date}.txt";
var lines = File.ReadAllLines(orderFileName);
foreach (var line in lines.Skip(1))
{
//If parsing any line returns false.
if (!IsValidLine(line))
return false;
//Or if you need to create a list of the valid Order entries.
if (IsValidLine(line))
{
var order = new Order();
//...
orderList.Add(newOrder);
}
}
return true;
}
Alternatives:
Add a static function in the Order class to parse a given line and return a new object of Order type if the line is valid. Something like this.
If its not too late, then consider using a local database or serialization. Something like this and maybe this if you don't mind a vb.net example.

You need to create this method an extension method. It should be defined in static class:
public static class ObjectExtensions
{
public static bool ArePropertiesNotNull<T>(this T obj)
{
return typeof(T).GetProperties().All(propertyInfo => propertyInfo.GetValue(obj) != null);
}
}

Evaluating boolean expression in C#

I have written the code below to evaluate a boolean expression. The expression is coded in the form of objects.
It's one of those moments when I look at the code and think: I'm sure there's a better way to code that, using less boolean variables but can't see the right way to go. Any help? Unit tests have been written and are passing for a variety of inputs.
if (tree == null || !tree.IsActive || tree.FilterNodes == null)
{
return false;
}
var result = false;
foreach (var filter in tree.FilterNodes.Where(a => a.IsActive && a.ConditionNodes != null))
{
var tempBool = false;
foreach (var condition in filter.ConditionNodes.Where(a => a.IsActive))
{
if (!string.IsNullOrWhiteSpace(condition.FieldName) && values.ContainsKey(condition.FieldName))
{
var value = values[condition.FieldName];
if (filter.LogicalOperator == LogicalOperator.Or && ApplyCondition(condition.ConditionOperator, value, condition.FieldValue))
{
tempBool = true;
break;
}
else if (filter.LogicalOperator == LogicalOperator.And)
{
tempBool = ApplyCondition(condition.ConditionOperator, value, condition.FieldValue);
if (!tempBool)
{
break;
}
}
else
{
tempBool = false;
}
}
else if (!string.IsNullOrWhiteSpace(condition.FieldName) && filter.LogicalOperator == LogicalOperator.And)
{
tempBool = false;
}
}
result = tempBool;
if (!result)
{
break;
}
}
return result;

You could set tempBool = false first thing in the loop and leave out the else and last else if:
foreach (var condition in filter.ConditionNodes.Where(a => a.IsActive))
{
tempBool = false;
if (!string.IsNullOrWhiteSpace(condition.FieldName) && values.ContainsKey(condition.FieldName))
{
var value = values[condition.FieldName];
if (filter.LogicalOperator == LogicalOperator.Or && ApplyCondition(condition.ConditionOperator, value, condition.FieldValue))
{
tempBool = true;
break;
}
else if (filter.LogicalOperator == LogicalOperator.And)
{
tempBool = ApplyCondition(condition.ConditionOperator, value, condition.FieldValue);
if (!tempBool)
{
break;
}
}
}
}
EDIT
It gets even simpler:
foreach (var condition in filter.ConditionNodes.Where(a => a.IsActive))
{
tempBool = false;
if (!string.IsNullOrWhiteSpace(condition.FieldName) && values.ContainsKey(condition.FieldName))
{
var value = values[condition.FieldName];
tempBool == ApplyCondition(condition.ConditionOperator, value, condition.FieldValue);
if ((filter.LogicalOperator == LogicalOperator.And && !tempBool) || (filter.LogicalOperator == LogicalOperator.Or && tempBool))
{
break;
}
}
}
In the if you need ApplyCondition to be true and then set tempBool to true (also the result of ApplyCondition). In the else if you set tempBoolto the result of ApplyCondition. That means you can set tempBoolto the result of ApplyConditionin the first place. Now you just need to decide if you need to break.

Taking a more o-o approach, I think your operators need to be defined by classes that inherit from a base class. The base class would have an abstract Evaluate method that your operators implement. You can then use o-o polymorphism to evaluate your operators without worrying about the internal details. Effectively you have the beginnings of a simple interpreter.

A more formal way to code a boolean interpreter is considering a boolean expression as generated by a formal grammar and writing a parser and an interpreter for it. The interpreter could be implemented as an abstract syntax tree.
I made an open source library to achieve this, if you want you can take a look on GitHub.

Convert String To Int in LINQ

I have a LINQ query that queries a DataTable. In the DataTable, the field is a string and I need to compare that to an integer, basically:
if ((electrical >= 100 && electrical <= 135) || electrical == 19)
{
// The device passes
}
the problem is, I am trying to do this in LINQ like this:
var eGoodCountQuery =
from row in singulationOne.Table.AsEnumerable()
where (Int32.Parse(row.Field<String>("electrical")) >= 100 &&
Int32.Parse(row.Field<String>("electrical")) <= 135) &&
Int32.Parse(row.Field<String>("electrical")) != 19 &&
row.Field<String>("print") == printName
select row;
I keep getting the exception:
Input string was not in a correct format
The main problem occurs when electrical == ""

Unfortunately, the framework doesn't provide a nice clean way to handle parsing scenarios where it fails. Of what's provided, they only throw exceptions or use out parameters, both of which does not work well with linq queries. If any one value you're parsing fails, the entire query fails and you just can't really use out parameters. You need to provide a method to handle the parsing without that does not throw and does not require using out parameters.
You can handle this in many ways. Implement it where upon failure, you return some default sentinel value.
public static int ParseInt32(string str, int defaultValue = 0)
{
int result;
return Int32.TryParse(str, out result) ? result : defaultValue;
}
Or what I would recommend, return a nullable value (null indicating it failed).
public static int? ParseInt32(string str)
{
int result;
return Int32.TryParse(str, out result) ? result : null;
}
This simplifies your query dramatically while still leaving it readable.
public bool GetElectricalStatus(string printName)
{
var query =
from row in singulationOne.Table.AsEnumerable()
where row.Field<string>("print") == printName
// using the nullable implementation
let electrical = ParseInt32(row.Field<string>("electrical"))
where electrical != null
where electrical == 19 || electrical >= 100 && electrical <= 135
select row;
return !query.Any();
}
p.s., your use of the Convert.ToInt32() method is incorrect. It is the same as calling Int32.Parse() and does not return a nullable, it will throw on failure.

I would check if the data in the column does not contain leading/trailing whitespaces - i.e. "15 " rather than "15" and if it does (or might do) trim it before trying to convert:
Int32.Parse(row.Field<String>("electrical").Trim())
BTW: not related to the error but I'd use let statement to introduce a local variable and do the conversion once:
let x = Int32.Parse(row.Field<String>("electrical").Trim())
where x >= 100...

I could not get anything to work, so I re-did the whole method:
public bool GetElectricalStatus(string printName)
{
List<object> eGoodList = new List<object>();
var eGoodCountQuery =
from row in singulationOne.Table.AsEnumerable()
where row.Field<String>("print") == printName
select row.Field<String>("electrical");
foreach (var eCode in eGoodCountQuery)
{
if (!string.IsNullOrEmpty(eCode.ToString()))
{
int? eCodeInt = Convert.ToInt32(eCode);
if (eCodeInt != null &&
(eCodeInt >= 100 && eCodeInt <= 135) || eCodeInt == 19)
{
eGoodList.Add(eCode);
}
}
}
if (eGoodList.Count() > 0)
{
return false;
}
else
{
return true;
}
}
The main problem occurs when electrical == ""

Why not make a function that does your evaluation, and call it in your Linq query. Put logic in to check the validity of the data contained within (so if you can't parse the data, it should return false)...
The function:
bool IsInRange(string text, int lower, int upper, params int[] diqualifiers)
{
int value = int.MinValue;
if (!int.TryParse(text, out value)) {
return false;
}
if (!(value >= lower && value <= upper)) {
return false;
}
if (disqualifiers != null && disqualifiers.Any(d => d == value)) {
return false;
}
return true;
}
The Linq query...
var eGoodCountQuery =
from row in singulationOne.Table.AsEnumerable()
where
IsInRange(row.Field<String>("electrical"), 100, 135, 19)
&& row.Field<String>("print") == printName
select row;

A function to convert null to string

I want to create a function to convert any null value e.g. from a database to an empty string.
I know there are methods such as if value != null ?? value : String.Empty but is there a way to pass null to a method e.g.
public string nullToString(string? value)
{
if(value == null) return empty;
return value
}
But I am not sure on the parameter syntax to do this.
I tried the above but it says not a nullable type.

static string NullToString( object Value )
{
// Value.ToString() allows for Value being DBNull, but will also convert int, double, etc.
return Value == null ? "" : Value.ToString();
// If this is not what you want then this form may suit you better, handles 'Null' and DBNull otherwise tries a straight cast
// which will throw if Value isn't actually a string object.
//return Value == null || Value == DBNull.Value ? "" : (string)Value;
}

When you get a NULL value from a database, the value returned is DBNull.Value on which case, you can simply call .ToString() and it will return ""
Example:
reader["Column"].ToString()
Gets you "" if the value returned is DBNull.Value
If the scenario is not always a database, then I'd go for an Extension method:
public static class Extensions
{
public static string EmptyIfNull(this object value)
{
if (value == null)
return "";
return value.ToString();
}
}
Usage:
string someVar = null;
someVar.EmptyIfNull();

Convert.ToString(object) converts to string. If the object is null, Convert.ToString converts it to an empty string.
Calling .ToString() on an object with a null value throws a System.NullReferenceException.
EDIT:
Two exceptions to the rules:
1) ConvertToString(string) on a null string will always return null.
2) ToString(Nullable<T>) on a null value will return "" .
Code Sample:
// 1) Objects:
object obj = null;
//string valX1 = obj.ToString(); // throws System.NullReferenceException !!!
string val1 = Convert.ToString(obj);
Console.WriteLine(val1 == ""); // True
Console.WriteLine(val1 == null); // False
// 2) Strings
String str = null;
//string valX2 = str.ToString(); // throws System.NullReferenceException !!!
string val2 = Convert.ToString(str);
Console.WriteLine(val2 == ""); // False
Console.WriteLine(val2 == null); // True
// 3) Nullable types:
long? num = null;
string val3 = num.ToString(); // ok, no error
Console.WriteLine(num == null); // True
Console.WriteLine(val3 == ""); // True
Console.WriteLine(val3 == null); // False
val3 = Convert.ToString(num);
Console.WriteLine(num == null); // True
Console.WriteLine(val3 == ""); // True
Console.WriteLine(val3 == null); // False

You can just use the null coalesce operator.
string result = value ?? "";

Its possible to make this even shorter with C# 6:
public string NullToString(string value)
{
return value?.ToString() ?? string.empty;
}

Sometimes I just append an empty string to an object that might be null.
object x = null;
string y = (x + "").ToString();
This will never throw an exception and always return an empty string if null and doesn't require if then logic.

public string nullToString(string value)
{
return value == null ?string.Empty: value;
}

You can use Convert.ToString((object)value). You need to cast your value to an object first, otherwise the conversion will result in a null.
using System;
public class Program
{
public static void Main()
{
string format = " Convert.ToString({0,-20}) == null? {1,-5}, == empty? {2,-5}";
object nullObject = null;
string nullString = null;
string convertedString = Convert.ToString(nullObject);
Console.WriteLine(format, "nullObject", convertedString == null, convertedString == "");
convertedString = Convert.ToString(nullString);
Console.WriteLine(format, "nullString", convertedString == null, convertedString == "");
convertedString = Convert.ToString((object)nullString);
Console.WriteLine(format, "(object)nullString", convertedString == null, convertedString == "");
}
}
Gives:
Convert.ToString(nullObject ) == null? False, == empty? True
Convert.ToString(nullString ) == null? True , == empty? False
Convert.ToString((object)nullString ) == null? False, == empty? True
If you pass a System.DBNull.Value to Convert.ToString() it will be converted to an empty string too.

It is possible to use the "?." (null conditional member access) with the "??" (null-coalescing operator) like this:
public string EmptyIfNull(object value)
{
return value?.ToString() ?? string.Empty;
}
This method can also be written as an extension method for an object:
public static class ObjectExtensions
{
public static string EmptyIfNull(this object value)
{
return value?.ToString() ?? string.Empty;
}
}
And you can write same methods using "=>" (lambda operator):
public string EmptyIfNull(object value)
=> value?.ToString() ?? string.Empty;

you can use ??""
for example:
y=x??""
if x isn't null y=x but if x is null y=""

1. string.Format
You can use string.Format which converts null to empty string
string nullstr = null;
string quotestring = string.Format("{0}", nullstr);
Console.WriteLine(quotestring);//Output- ""
2.string interpolation
or you can use string interpolation. this feature is available in C# 6 and later versions.
InterpolatedExpression produces a result to be formatted. A string representation of the null result is String.Empty.
string nullstr = null;
string quotestring = $"{nullstr}";
Console.WriteLine(quotestring);//Output- ""

public string ToString(this string value)
{
if (value == null)
{
value = string.Empty;
}
else
{
return value.Trim();
}
}

Its an old topic, but there is a "elegant" way to do that...
static string NullToString( object Value )
{
return Value = Value ?? string.Empty;
}

You can try this
public string ToString(this object value)
{
// this will throw an exception if value is null
string val = Convert.ToString (value);
// it can be a space
If (string.IsNullOrEmpty(val.Trim())
return string.Empty:
}
// to avoid not all code paths return a value
return val;
}

you can use null-coalescing-operator C# 8.0 and later
value ??=string.Empty;
??= operators

Assign a nullable string to string.
string? input = "kushal";
string output = input?.ToString() ?? ""

According to the following MSDN page, you need the Convert.ToString method
string x = Convert.ToString((object)value)

Determine value of object in C#

What would be the best way to determine if an object equals number zero (0) or string.empty in C#?
EDIT: The object can equal any built-in System.Value type or reference type.
Source Code:
public void MyMethod(object input1, object input2)
{
bool result = false;
object compare = new object();
if(input != null && input2 != null)
{
if(input1 is IComparable && input2 is IComparable)
{
//do check for zero or string.empty
//if input1 equals to zero or string.empty
result = object.Equals(input2);
//if input1 not equals to zero or string.empty
result = object.Equals(input1) && object.Equals(input2); //yes not valid, but this is what I want to accomplish
}
}
}

Using Jonathan Holland code sample with a minor modification, here is the solution that worked:
static bool IsZeroOrEmpty(object o1)
{
bool Passed = false;
object ZeroValue = 0;
if(o1 != null)
{
if(o1.GetType().IsValueType)
{
Passed = (o1 as System.ValueType).Equals(Convert.ChangeType(ZeroValue, o1.GetType()))
}
else
{
if (o1.GetType() == typeof(String))
{
Passed = o1.Equals(String.Empty);
}
}
}
return Passed;
}

What's wrong with this?
public static bool IsZeroOrEmptyString(object obj)
{
if (obj == null)
return false;
else if (obj.Equals(0) || obj.Equals(""))
return true;
else
return false;
}

Michael, you need to provide a little bit more information here.
strings can be compared to null or string.Empty by using the method
string x = "Some String"
if( string.IsNullOrEmpty(string input) ) { ... }
int, decimals, doubles (and other numeric value-types) can be compared to 0 (zero) with a simple == test
int x = 0;
if(x == 0) { ... }
You can also have nullable value-types also by using the ? operator when you instantiate them. This allows you to set a value type as null.
int? x = null;
if( !x.HasValue ) { }
For any other object, a simple == null test will tell you if its null or not
object o = new object();
if( o != null ) { ... }
Hope that sheds some light on things.

Not quite sure the reasoning behind this, because .Equals is reference equality on reference types, and value equality on value types.
This seems to work, but I doubt its what you want:
static bool IsZeroOrEmpty(object o1)
{
if (o1 == null)
return false;
if (o1.GetType().IsValueType)
{
return (o1 as System.ValueType).Equals(0);
}
else
{
if (o1.GetType() == typeof(String))
{
return o1.Equals(String.Empty);
}
return o1.Equals(0);
}
}

Do you mean null or string.empty, if you're talking about strings?
if (String.IsNullOrEmpty(obj as string)) { ... do something }
Oisin

In the first case by testing if it is null. In the second case by testing if it is string.empty (you answered your own question).
I should add that an object can never be equal to 0. An object variable can have a null reference though (in reality that means the variable has the value of 0; there is no object in this case though)

obj => obj is int && (int)obj == 0 || obj is string && (string)obj == string.Empty