I am trying to match a string typed in by a user to a string in a database.
Before I try match them i need to take the spaces out both of them.
how do i do this?
public static Product GetProductbypart(ModelContainer context, string partnumber)
{
var query = from product in context.Products
where product.Partnumber == partnumber
select product;
return query.FirstOrDefault();
}
this is my query which works if the user types in the exact part number. But some users may type it in with too many spaces or too less.
I want to take the partnumber take out the spaces. Then take the product.Partnumber and take of the spaces of that also, to see if there is a match.
Sample inputs:
MC-9a 1a AC24V
MC-9a 50/60Hz
1
123
MC+123-1
F6h67e
_8jj+j7s
string partnumber = partnumber.Replace(" ", String.Emtpy);
var query = from product in context.Products
where product.Partnumber.Replace("", String.Empty) == partnumber
select product;
This removes spaces in the strings product.Partnumber and partnumber. However, if you use linq-to-SQL the part product.Partnumber.Replace(..) won't work. But I'm not sure why you have to remove spaces of the product number in the database. Sounds like inconsistent data to me.
public static Product GetProductbypart(ModelContainer context, string partnumber)
{
partnumber = partnumber.Replace(" ", String.Empty);
var products = from product in context.Products
select product;
foreach(var item in products)
{
if (item.Partnumber != null)
{
item.Partnumber = item.Partnumber.Replace(" ", String.Empty);
if (item.Partnumber == partnumber)
{
var query = from product in context.Products
where product.Id == item.Id
select product;
return query.FirstOrDefault();
}
}
}
return null;
}
This is how i did it
In this case I would think about implementing it a little bit differently. If you need your table only in order to compare it with the user input, you can remove spaces in the database in advance, before running the query. Also there is no point in removing spaces in database, you can do it in client code.
In this case you will be able to use regular Equals and also it should be a little bit more efficient.
I think the best answer here is to not try and figure out how the user entered the data, instead make sure that they entered a valid part number in the first place. Can you provide some form of input format? Even if it means using hyphens where spaces are, you can always remove them before you check, but at least you'll have data in the correct format.
Related
I'm trying to update a record given the customer Id, the row Id, and a dynamic column name.
Thus far I have the following, with the trouble spot marked by ***:
public void UpdateRecord(int Id, string rval, string column, string value)
{
var rId = GetRvalId(rval);
var entry = _context.Customers
.Where(x => x.Id == Id && x.RVals.Id == rId && x.***column?*** == column).First();
entry = value;
}
I haven't been able to find a good example of how to do this.
Addition after comments at the end
The reason you couldn't find examples is because it is not a good design.
Your method is very error prone, difficult to test and horrible to maintain. What if someone types the incorrect column name? What if you try to assign a string to the customer's birthday? And even if you would implement some string checking for column names and proposed values, then your program wouldn't work anymore after someone changes the names or the types of the columns.
So let's redesign!
Apparently you have a Customer with an Id and a property Rvals. This property Rvals also has a property Id.
You also have a function GetRValId that can convert a string rval to an int rvalId.
What you want, is given an Id and a string rval, you want to update one of the columns of the first Customer with this Idand rValId.
Side questions: Can there be more than one Customer with Id? In that case: are you sure Id is an ID? What do you want if there are more matching Customers? Update all customers or update only the first one? Which customer do you define as the first customer?
Leaving the side questions aside. We want a function signature that reports errors at compile time if you use non-existing customer properties, or if you try to assign a string to a Birthday. Something like this perhaps?
Update the name of the customer:
int customerId = ...
string rval = ...
string proposedName = "John Doe";
UpdateCustomerRecord(id, rval, customer => customer.Name = proposedName);
Update the Birthday of the customer:
DateTime proposedBirthday = ...
UpdateCustomerRecord(id, rval, customer => customer.Birthday = proposedBirthday)
This way you can't use any column that does not exist, and you can't assign a string to a DateTime.
You want to change two values in one call? Go ahead:
UpdateCustomerRecord(id, rval, customer =>
{
customer.Name = ...;
customer.Birthday = ...;
});
Convinced? Let's write the function:
public void UpdateCustomerRecord(int customerId, string rval, Action<Customer> action)
{
// the beginning is as in your function:
var rId = GetRvalId(rval);
// get the customer that you want to update:
using (var _Context = ...)
{
// get the customer you want to update:
var customerToUpdate = _Context.Customers
.Where(customer => customer.Id == Id
&& customer.RVals.Id == rId)
.FirstOrDefault();
// TODO: exception if there is no customerToUpdate
// perform the action and save the changes
action(customerToUpdate);
_context.SaveChanges();
}
Simple comme bonjour!
Addition after comments
So what does this function do? As long as you don't call it, it does nothing. But when you call it, it fetches a customer, performs the Action on the Customer you provided in the call, and finally calls SaveChanges.
It doesn't do this with every Customer, no it does this only with the Customer with Id equal to the provided Id and customer.RVals.Id == ... (are you still certain there is more than one customer with this Id? If there is only one, why check for RVals.Id?)
So the caller not only has to provide the Id, and the RVal, which define the Customer to update, but he also has to define what must be done with this customer.
This definition takes the form of:
customer =>
{
customer.Name = X;
customer.BirthDay = Y;
}
Well if you want, you can use other identifiers than customer, but it means the same:
x => {x.Name = X; x.BirthDay = Y;}
Because you put it on the place of the Action parameter in the call to UpdateCustomerRecord, I know that x is of type Customer.
The Acton statement means: given a customer that must be updated, what must we do with the customer? You can read it as if it was a Function:
void Action(Customer customer)
{
customer.Name = ...
customer.BirthDay = ...
}
In the end it will do something like:
Customer customerToUpdate = ...
customerToUpdate.Name = X;
customerToUpdate.BirthDay = Y;
SaveChanges();
So in the third parameter, called Action you can type anything you want, even call functions that have nothing to do with Customers (probably not wise). You have an input parameter of which you are certain that it is a Customer.
See my earlier examples of calling UpdateCustomerRecord, one final example:
UpdateCustomerRecord( GetCustomerId(), GetCustomerRVal,
// 3rd parameter: the actions to perform once we got the customerToUpdate:
customer =>
{
DateTime minDate = GetEarliestBirthDay();
if (customer.BirthDay < minDate)
{ // this Customer is old
customer.DoThingsThatOldPeopleDo();
}
else
{ // this Customer is young
customer.DoThingsThatYoungPeopleDo();
}
}
}
So the Action parameter is just a simpler way to say: "once you've got the Customer that must be updated, please perform this function with the Customer
So if you only want to update a given property of the customer write something like:
UpdateCustomerRecord(... , customer =>
{
Customer.PropertyThatMustBeUpdated = NewValueOfProperty;
}
Of course this only works if you know which property must be updated. But since you wrote "I am trying to update a specific cell." I assume you know which property the cells in this column represent.
It is not possible to pass the column name as the string value in LINQ. Alternate way to do it, if you have the limited number of the column name which can be passed then it can be achieved as below:
public void UpdateRecord(int Id, string rval, string column, string value)
{
var rId = GetRvalId(rval);
var entry = _context.Customers
.Where(x => x.Id == Id &&
x.RVals.Id == rId &&
(x.column1 == value || column == column1) &&
(x.column2 == value || column == column2) &&
(x.column3 == value || column == column3) &&
(x.column4 == value || column == column4) &&
(x.column5 == value || column == column5) &&
)).First();
entry = value;
}
UpdateRecord(5, "rval", "column1", "value");
UpdateRecord(5, "rval", "column2", "value");
UpdateRecord(5, "rval", "column3", "value");
Here, suppose you have the 5 columns that can be passed while calling the funcion UpdateRecord then you can add the 5 clauses in the WHERE as above.
Other way to do it dynamic LINQ
var entry = db.Customers.Where(column + " = " + value).Select(...);
I have some errors using Linq on DataTable and I couldn't figure it out how to solve it. I have to admit that i am pretty new to Linq and I searched the forum and Internet and couldn't figure it out. hope you can help.
I have a DataTable called campaign with three columns: ID (int), Product (string), Channel (string). The DataTable is already filled with data. I am trying to select a subset of the campaign records which satisfied the conditions selected by the end user. For example, the user want to list only if the Product is either 'EWH' or 'HEC'. The selection criteria is dynaically determined by the end user.
I have the following C# code:
private void btnClick()
{
IEnumerable<DataRow> query =
from zz in campaign.AsEnumerable()
orderby zz.Field<string>("ID")
select zz;
string whereClause = "zz.Field<string>(\"Product\") in ('EWH','HEC')";
query = query.Where(whereClause);
DataTable sublist = query.CopyToDataTable<DataRow>();
}
But it gives me an error on line: query = query.Where(whereClause), saying
No property or field 'zz' exists in type 'DataRow'".
If I changed to:
string whereClause = "Product in ('EWH','HEC')"; it will say:
No property or field 'Product' exists in type 'DataRow'
Can anyone help me on how to solve this problem? I feel it could be a pretty simple syntax change, but I just don't know at this time.
First, this line has an error
orderby zz.Field<string>("ID")
because as you said, your ID column is of type int.
Second, you need to learn LINQ query syntax. Forget about strings, the same way you used from, orderby, select in the query, you can also use where and many other operators. Also you'll need to learn the equivalent LINQ constructs for SQL-ish things, like for instance IN (...) is mapped to Enumerable.Contains etc.
With all that being said, here is your query
var productFilter = new[] { "EWH", "HEC" };
var query =
from zz in campaign.AsEnumerable()
where productFilter.Contains(zz.Field<string>("Product"))
orderby zz.Field<int>("ID")
select zz;
Update As per your comment, if you want to make this dynamic, then you need to switch to lambda syntax. Multiple and criteria can be composed by chaining multiple Where clauses like this
List<string> productFilter = ...; // coming from outside
List<string> channelFilter = ...; // coming from outside
var query = campaign.AsEnumerable();
// Apply filters if needed
if (productFilter != null && productFilter.Count > 0)
query = query.Where(zz => productFilter.Contains(zz.Field<string>("Product")));
if (channelFilter != null && channelFilter.Count > 0)
query = query.Where(zz => channelFilter.Contains(zz.Field<string>("Channel")));
// Once finished with filtering, do the ordering
query = query.OrderBy(zz => zz.Field<int>("ID"));
Basically all I'm looking to do is something like the following:
string EntityFrameworkType = "Product";
string searchField = "ProductName";
string searchValue = "My Product";
using( var context = new entitycontext())
{
var result = (from x in context.EntityFrameworkType.Where(l=>l.searchField == searchValue) select x).FirstOrDefault();
}
of course this syntax won't work because context does not contain an entity called "EntityFrameworkType"...
Is it possible to do this another way??? What I'm looking to do in generalize my database duplicate check. In this example, I'm searching for any Product with the Name "My Product". But I'd like to be able to pass in these string for say, ProductCategory with ProductCategoryId = 1.... etc...
you can have a look here to get the idea of how it is done.
You'll need to learn about Expression
I am trying to select some records using LINQ for Entities (EF4 Code First).
I have a table called Monitoring with a field called AnimalType which has values such as
"Lion,Tiger,Goat"
"Snake,Lion,Horse"
"Rattlesnake"
"Mountain Lion"
I want to pass in some values in a string array (animalValues) and have the rows returned from the Monitorings table where one or more values in the field AnimalType match the one or more values from the animalValues. The following code ALMOST works as I wanted but I've discovered a major flaw with the approach I've taken.
public IQueryable<Monitoring> GetMonitoringList(string[] animalValues)
{
var result = from m in db.Monitorings
where animalValues.Any(c => m.AnimalType.Contains(c))
select m;
return result;
}
To explain the problem, if I pass in animalValues = { "Lion", "Tiger" } I find that three rows are selected due to the fact that the 4th record "Mountain Lion" contains the word "Lion" which it regards as a match.
This isn't what I wanted to happen. I need "Lion" to only match "Lion" and not "Mountain Lion".
Another example is if I pass in "Snake" I get rows which include "Rattlesnake". I'm hoping somebody has a better bit of LINQ code that will allow for matches that match the exact comma delimited value and not just a part of it as in "Snake" matching "Rattlesnake".
This is a kind of hack that will do the work:
public IQueryable<Monitoring> GetMonitoringList(string[] animalValues)
{
var values = animalValues.Select(x => "," + x + ",");
var result = from m in db.Monitorings
where values.Any(c => ("," + m.AnimalType + ",").Contains(c))
select m;
return result;
}
This way, you will have
",Lion,Tiger,Goat,"
",Snake,Lion,Horse,"
",Rattlesnake,"
",Mountain Lion,"
And check for ",Lion," and "Mountain Lion" won't match.
It's dirty, I know.
Because the data in your field is comma delimited you really need to break those entries up individually. Since SQL doesn't really support a way to split strings, the option that I've come up with is to execute two queries.
The first query uses the code you started with to at least get you in the ballpark and minimize the amount of data you're retrieving. It converts it to a List<> to actually execute the query and bring the results into memory which will allow access to more extension methods like Split().
The second query uses the subset of data in memory and joins it with your database table to then pull out the exact matches:
public IQueryable<Monitoring> GetMonitoringList(string[] animalValues)
{
// execute a query that is greedy in its matches, but at least
// it's still only a subset of data. The ToList()
// brings the data into memory, so to speak
var subsetData = (from m in db.Monitorings
where animalValues.Any(c => m.AnimalType.Contains(c))
select m).ToList();
// given that subset of data in the List<>, join it against the DB again
// and get the exact matches this time
var result = from data in subsetData
join m in db.Monitorings on data.ID equals m.ID
where data.AnimalType.Split(',').Intersect(animalValues).Any ()
select m;
return result;
}
I'm very new to Linq, I can find multi-line data reading examples everywhere (by using foreach()), but what is the correct way of reading a single line of data? Like a classic Product Detail page.
Below is what I tried:
var q = from c in db.Products
where c.ProductId == ProductId
select new { c.ProductName, c.ProductDescription, c.ProductPrice, c.ProductDate };
string strProductName = q.First().ProductName.ToString();
string strProductDescription = q.First().ProductDescription.ToString();
string strProductPrice = q.First().ProductPrice.ToString();
string strProductDate = q.First().ProductDate.ToString();
The code looks good to me, but when I see the actual SQL expressions generated by using SQL Profiler, it makes me scared! The program executed four Sql expressions and they are exactly the same!
Because I'm reading four columns from a single line. I think I must did something wrong, so I was wondering what is the right way of doing this?
Thanks!
Using the First() extension method would throw the System.InvalidOperationException when no element in a sequence satisfies a specified condition.
If you use the FirstOrDefault() extension method, you can test against the returned object to see if it's null or not.
FirstOrDefault returns the first element of a sequence, or a default value if the sequence contains no elements; in this case the default value of a Product should be null. Attempting to access the properties on this null object will throw ArgumentNullException
var q = (from c in db.Products
where c.ProductId == ProductId
select new { c.ProductName, c.ProductDescription, c.ProductPrice, c.ProductDate }).FirstOrDefault();
if (q != null)
{
string strProductName = q.ProductName;
string strProductDescription = q.ProductDescription;
string strProductPrice = q.ProductPrice;
string strProductDate = q.ProductDate;
}
Also, you shouldn't have to cast each Property ToString() if you're object model is setup correctly. ProductName, ProductDescription, etc.. should already be a string.
The reason you're getting 4 separate sql queries, is because each time you call q.First().<PropertyHere> linq is generating a new Query.
var q = (from c in db.Products
where c.ProductId == ProductId
select new { c.ProductName, c.ProductDescription, c.ProductPrice, c.ProductDate }
).First ();
string strProductName = q.ProductName.ToString();
string strProductDescription = q.ProductDescription.ToString();
string strProductPrice = q.ProductPrice.ToString();
string strProductDate = q.ProductDate.ToString();