We Keep Coding

Constructing a insert query based on a LINQ query

I am trying to build a sql insert query based on the number of filled out textboxes returned from a LINQ query. Basically, the start of the textboxes start at the tab index number 13 and ends at the tab index number 33 and adds the non empty textboxes to a keyvaluepair list. The issue that I am confused about is how to add the filled out textboxes' values to named parameters inside the insert query without having a error of number of query values and destination fields are not the same. Here is the code I have in place:
// use LINQ to fetch all the children textboxes based on the ones that are not empty
System.Collections.Generic.Dictionary<string, string> dictionary = tabCtrl1.TabPages["tabPage1"].Controls.OfType<TextBox>()
.Where(t => t.TabIndex >= startTabIndex && t.TabIndex <= endTabIndex && !string.IsNullOrWhiteSpace(t.Text))
.Select(x => new System.Collections.Generic.KeyValuePair<string, string>(x.Name, x.Text))
.ToDictionary(z => z.Key, z => z.Value);
// loop through all the children textboxes
// and assign them to the list members.childTextBoxes
foreach (System.Collections.Generic.KeyValuePair<string, string> kvp in dictionary)
{
members.childTextBoxes.Add(new System.Collections.Generic.KeyValuePair<string, string>($"{kvp.Key}", $"{kvp.Value}"));
}
and then constructing of the insert query:
for (int i = 0; i < members.childTextBoxes.Count; i++)
{
using (members.DBCommand = new System.Data.OleDb.OleDbCommand("INSERT INTO children (pid, childName, birthday, childEmail)" +
"VALUES (" + lastInsertId + ", #" + members.childTextBoxes[i].Key + ")", members.DBConnection))
{
members.DBCommand.Parameters.AddWithValue("#" + members.childTextBoxes[i].Key, members.childTextBoxes[i].Value);
}
// error occurs here. i'm assuming its to do
if (members.DBCommand.ExecuteNonQuery() > 0)
{
MessageBox.Show("Records inserted", "QBC", MessageBoxButtons.OK);
}
}
}
I hope this is enough information that describes the problem I am confused about.
Any help would be appreciated.
Thanks!
I can try to add more information if it helps make my question more clear.
update-
I went ahead and tried to use .Add instead of .AddWithValue but unfortunately that kept giving me an insert into query syntax error.
Here is the updated code for the insert query builder:
string fieldList = $"{string.Join(",", members.childTextBoxes.Select(tb => mapToDatabase[tb.Key]))}";
string valueList = $"{string.Join(",", members.childTextBoxes.Select(tb => "?"))}";
string insertQuery = $"INSERT INTO children {fieldList} VALUES {valueList}";
using (members.DBCommand = new System.Data.OleDb.OleDbCommand(insertQuery, members.DBConnection))
{
foreach (var field in members.childTextBoxes)
{
members.DBCommand.Parameters.Add("#" + field.Key, OleDbType.LongVarChar).Value = field.Value;
}
if (members.DBCommand.ExecuteNonQuery() > 0) // error occurs here
{
MessageBox.Show("Records inserted", "QBC", MessageBoxButtons.OK);
}
}

The best I can tell from the code you are showing in your question, you would want something like this:
var controlMap = new Dictionary<string, string>();
controlMap.Add(nameof(txtChildName), "ChildName");
controlMap.Add(nameof(txtParentName), "ParentName");
string fieldList = $"({string.Join(",", childTextBoxes.Select(tb => controlMap[tb.Key]))})" ;
string valueList = $"({string.Join(",", childTextBoxes.Select(tb => "?"))})";
string insertStatement = $"INSERT INTO children {fieldList} VALUES {valueList}";
var command = new OleDbCommand(insertStatement, members.DBConnection);
foreach (var field in childTextBoxes)
{
command.Parameters.Add(field.Value);
}
OleDbCommand doesn't support named parameters, so you have to use positional ones. They are marked with an "?", and added in the order they are used.
You also need to build both the field list, and the values list in the SQL insert statement, so that that order of fields in your field list matches the order that the "?" markers will be populated when you add the parameters.
I haven't been able to test this, since I don't have your full setup, but it should get you pretty close. It assumes that childTextBoxes is declared as List<KeyValuePair<string, string>> since I can't see your actual declaration. You may have to adjust that a bit if it isn't correct.

fixed the error, I had to enclose the insert values with parenthesis.
string insertQuery = $"INSERT INTO children (pid, {fieldList}) VALUES (?,{valueList})";
that fixed it.

Getting Id during sql query and using for another Insert Statment

So I have been creating a library that uses dapper and allows user to manipulate a database.
I need some help with finding the best way to achieve the following.
Lets say I have an "order" table and I have a "transaction" table and an "order_line" table.
I want to take the Increment Id of table "order" when inserting and use it to store it in a column in "transaction" and "order_line" table and I want all of this done in a SQL transaction so that I can roll back in case of any issue.
Now since my library is dynamic to any type and action, I am not sure on how to approach something like this.
Here is the code on how you would insert:
I have 2 global variables
private string connectionString { get; set; }
public void newConnection(string connection)
{
if (string.IsNullOrWhiteSpace(connectionString))
{
connectionString = connection;
}
}
private List<KeyValuePair<string, object>> transactions = new List<KeyValuePair<string, object>>();
Here is how you call to have a class to be saved to the database:
public void Add(object item)
{
string propertyNames = "";
string propertyParamaters = "";
Type itemType = item.GetType();
System.Reflection.PropertyInfo[] properties = itemType.GetProperties();
for (int I = 0; I < properties.Count(); I++)
{
if (properties[I].Name.Equals("Id", StringComparison.CurrentCultureIgnoreCase) || properties[I].Name.Equals("AutoId", StringComparison.CurrentCultureIgnoreCase))
{
continue;
}
if (I == properties.Count() - 1)
{
propertyNames += "[" + properties[I].Name + "]";
propertyParamaters += "#" + properties[I].Name;
}
else
{
propertyNames += "[" + properties[I].Name + "],";
propertyParamaters += "#" + properties[I].Name + ",";
}
}
string itemName = itemType.Name;
KeyValuePair<string, object> command = new KeyValuePair<string, object>($"Insert Into[{ itemName}] ({ propertyNames}) Values({ propertyParamaters})", item);
transactions.Add(command);
}
There are more methods and like edit, remove, edit list, remove list etc. but are not relevant in this case.
When you want to commit changes to the database you call:
public void SaveChanges()
{
using (SqlConnection sqlConnection = new SqlConnection(connectionString))
{
sqlConnection.Open();
using (SqlTransaction sqlTransaction = sqlConnection.BeginTransaction())
{
try
{
foreach (KeyValuePair<string, object> command in transactions)
{
sqlConnection.Execute(command.Key, command.Value, sqlTransaction);
}
sqlTransaction.Commit();
}
catch
{
sqlTransaction.Rollback();
throw;
}
finally
{
sqlConnection.Close();
transactions.Clear();
}
}
sqlConnection.Close();
}
transactions.Clear();
}
You can find my library at github.com
https://github.com/pietercdevries/Bamboo.Net

Can it be done... yes... should we be trying to do this ourselves... I wouldn't :) but lets try it any way.
Some ideas that can make this code simpler:
Define helper interfaces and force the data classes to implement them or use attribute declarations to specify id fields and foreign key references
Investigate Injection or code generation techniques so that you can get some of this 'dynamic' coding and lookup executed at compile time, not runtime.
I don't use Dapper and your SqlConnection.Execute() is an extension method I am not familiar with but I assume that it generates DbParameters from the passed in object and applies them to the SqlCommand when it gets executed. Hopefully dapper has some functions to extract the parameters, so that they can be used in this code example, or perhaps you can use some of these concepts and adapt them to your dapper code. I just want to acknowledge that upfront and that I have omitted any code example here that parameterises the objects when executing the commands.
This is the journey that the following snippets will go down
Prepare the generated SQL to capture the Id field
Output the Id value when we save changes
Iterate over all remaining objects in the array and set the foreign key values
Note: these code changes are not tested or exception handled for production, nor would I call this "best practice" its just to prove the concept and help out a fellow coder :)
You have already devised a convention for Id field tracking, lets extend that idea by preparing the sql statement to set the value of an output parameter:
NOTE: in MS SQL, please use SCOPE_IDENTITY() in preference to ##Identity.
What is the difference between Scope_Identity(), Identity(), ##Identity, and Ident_Current?
NOTE: because the generated statements are using parameters, and we are not yet reading the parameter values, we will not need to regenerate the saved SQL statements later after we have found an Id value to insert to other objects... phew...
public void Add(object item)
{
List<string> propertyNames = new List<string>();
Type itemType = item.GetType();
System.Reflection.PropertyInfo[] properties = itemType.GetProperties();
for (int I = 0; I < properties.Count(); I++)
{
if (properties[I].Name.Equals("Id", StringComparison.CurrentCultureIgnoreCase) || properties[I].Name.Equals("AutoId", StringComparison.CurrentCultureIgnoreCase))
{
continue;
}
propertyNames.Add(properties[I].Name);
}
string itemName = itemType.Name;
KeyValuePair<string, object> command = new KeyValuePair<string, object>
($"Insert Into[{itemName}] ({String.Join(",", propertyNames.Select(p => $"[{p}]"))}) Values({String.Join(",", propertyNames.Select(p => $"#{p}"))}); SET #OutId = SCOPE_IDENTITY();", item);
transactions.Add(command);
// Simply append your statement with a set command on an #id parameter we will add in SaveChanges()
}
In Save Changes, implement output parameter to capture the created Id, and if the Id was captured, save it back into the object that the command is associated to.
NOTE: this code snippet shows the references to the solution in item 3.
And the foreach was replaced with a for so we could do forward iterations from the current index
public void SaveChanges()
{
using (SqlConnection sqlConnection = new SqlConnection(connectionString))
{
sqlConnection.Open();
using (SqlTransaction sqlTransaction = sqlConnection.BeginTransaction())
{
try
{
for (int i = 0; i < transactions.Count; i++)
{
KeyValuePair<string, object> command = transactions[i];
// 1. Execute the command, but use an output parameter to capture the generated id
var cmd = sqlConnection.CreateCommand();
cmd.Transaction = sqlTransaction;
cmd.CommandText = command.Key;
SqlParameter p = new SqlParameter()
{
ParameterName = "#OutId",
Size = 4,
Direction = ParameterDirection.Output
};
cmd.Parameters.Add(p);
cmd.ExecuteNonQuery();
// Check if the value was set, non insert operations wil not set this parameter
// Could optimise by not preparing for the parameter at all if this is not an
// insert operation.
if (p.Value != DBNull.Value)
{
int idOut = (int)p.Value;
// 2. Stuff the value of Id back into the Id field.
string foreignKeyName = null;
SetIdValue(command.Value, idOut, out foreignKeyName);
// 3. Update foreign keys, but only in commands that we haven't execcuted yet
UpdateForeignKeys(foreignKeyName, idOut, transactions.Skip(i + 1));
}
}
sqlTransaction.Commit();
}
catch
{
sqlTransaction.Rollback();
throw;
}
finally
{
sqlConnection.Close();
transactions.Clear();
}
}
sqlConnection.Close();
}
transactions.Clear();
}
/// <summary>
/// Update the Id field of the specified object with the provided value
/// </summary>
/// <param name="item">Object that we want to set the Id for</param>
/// <param name="idValue">Value of the Id that we want to push into the item</param>
/// <param name="foreignKeyName">Name of the expected foreign key fields</param>
private void SetIdValue(object item, int idValue, out string foreignKeyName)
{
// NOTE: There are better ways of doing this, including using interfaces to define the key field expectations.
// This logic is consistant with existing code so that you are familiar with the concepts
Type itemType = item.GetType();
foreignKeyName = null;
System.Reflection.PropertyInfo[] properties = itemType.GetProperties();
for (int I = 0; I < properties.Count(); I++)
{
if (properties[I].Name.Equals("Id", StringComparison.CurrentCultureIgnoreCase) || properties[I].Name.Equals("AutoId", StringComparison.CurrentCultureIgnoreCase))
{
properties[I].SetValue(item, idValue);
foreignKeyName = $"{item.GetType().Name}_{properties[I].Name}";
break;
}
}
}
So now your objects have their Id's updated as they are inserted.
Now for the fun part... After updating the Id, you should now iterate through the other objects and update their foreign key fields.
How you go about this in reality depends a lot on what kind of assumptions/conventions you are ready enforce over the data that you are updating. For simplicity sake, lets say that all of the foreign keys that we need to update are named with the convention {ParentClassName}_{Id}.
That means that if in our example we just inserted a new 'Widget', then we can try to forcibly update all other objects in this transaction scope that have a field 'Widget_Id' (or 'Widget_AutoId')
private void UpdateForeignKeys(string foreignKeyName, int idValue, IEnumerable<KeyValuePair<string, object>> commands)
{
foreach(var command in commands)
{
Type itemType = command.Value.GetType();
var keyProp = itemType.GetProperty(foreignKeyName);
if(keyProp != null)
{
keyProp.SetValue(command.Value, idValue);
}
}
}
This is a very simplistic example of how you could go about updating foreign (or reference) keys in OPs data persistence library.
You have probably observed in reality that relational key fields are rarely consistently named using any convention, but even when conventions are followed, my simple convention would not support a table that had multiple references to parents of the same type, for example a Manifest in one of my client's apps has 3 links back to a user table:
public class Manifest
{
...
Driver_UserId { get; set; }
Sender_UserId { get; set; }
Receiver_UserId { get; set; }
...
}
You would need to evolve some pretty advanced logic to tackle all possible linkage combinations.
Some ORMs do this by setting the values as negative numbers, and decrementing the numbers each type a new type is added to the command collection. Then after an insert you only need to update key fields that held the faked negative number with the updated number. You still need to know which fields are key fields, but atleast you don't need to track the precise fields that form the ends of each relationship, we can track with the values.
I like how Entity Framework goes about it though, try inject this linkage information about the fields using attributes on the properties. You may have to invent your own, but it's a clean declarative concept that forces you to describe these relationships up front in the data model classes in a way that all sorts of logic can later take advantage of, not just for generating SQL statements.
I don't want tobe too critical of Dapper, but once you start to go down this path or manually managing referential integrity like this there is a point where you should consider a more enterprise ready ORM like Entity Framework or nHibernate. Sure they come with some baggage but those ORMs have really evolved into mature products that have been optimised by the community. I now have very little manually written or scripted code to customise any interactions with the RDBMS at all, which means much less code to test or maintain. (= less bugs)

It doesn't say which database you are using. If it is MSSQL you can do
var id = connection.Query<int?>("SELECT ##IDENTITY").SingleOrDefault();
after executing the Insert. That gives you the id of the last insert.

Iterate over Database table row and store values in a Dictionary?

I want to implement a Dictionary cache in my program. How can I store the database result seen in the image below in a Dictionary Collection ?
I want to iterate over the Database table and store the content of LanguageName and IsoCode columns in a Dictionary like this Dictionary<LanguageName,IsoCode>.
My database (ctlang) looks like this:
Here is my code:
private string GetLanguageForIsoCode(string isoCode)
{
//check the isocode column and return the corresponding language
using (var unitOfWork = dataAccessUnitOfWorkFactory.Create())
{
//need to call every time the sql query
string query = "SELECT languagename FROM ctlang WHERE isocode='" + isoCode + "'";
List<string> result = unitOfWork.OwEntities.Database.SqlQuery<string>(query).ToList();
if (result.FirstOrDefault() != null)
{
return result.FirstOrDefault();
}
//if language not available in Database, fallback to German as default language
Thread.CurrentThread.CurrentCulture = CultureInfo.GetCultureInfo("de");
//displayName = Deutsch
return CultureInfo.GetCultureInfo("de").NativeName;
}
}
Bonus question: How can I search for a key in a dictionary using the value ?

It is. There is no problem in returning a key by its value, the only issue would be that there could theoretically be more than one key assigned to that value, since the key is what matters. But in your particular case that should be no problem, since only one isocode represents one language. So there would be no problem to make it like that, with dictionary:
public Dictionary<string, string> languagesAndKeys = new Dictionary<string, string>(); //Create it
Then you can search for keys/values like that:
string myValueByKey = languagesAndKeys["myKey"]; //getting value by key is easy
string myKeyByValue = languagesAndKeys.FirstOrDefault(item => item.Value == "myValue").Key; //getting the key of the FIRST matching value/or returning the default type. You'll need a check to be sure.
Afterwards, you can easily load the data from the sql table into the dictionary. For this goal, you can either use a temporary datatable with dataadapter, which will work well as long as the table is not that big, or you can use a DataReader to loop trough rows in the sql table one by one. I'm gonna be using a temp DataTable:
string cmdText = "SELECT * FROM ctlang"; //As far as I saw your cmd text in the code example, you may still want to take a look tho
string connectionString = ""; //fill the connection string according to your SQL server data
SqlDataAdapter dataAdapter = new SqlDataAdapter(cmdText, connectionString);
DataTable dTable = new DataTable();
dataAdapter.Fill(dTable);
foreach(DataRow row in dTable.Rows)
languagesAndKeys.Add(row[1].ToString(), row[0].ToString());//second column as a key, first column as a value - just like the structure of your table.

This is how I solved the problem. In my Database the Table with the languages is named CTLANG and the columns are LANGUAGENAME and ISOCODE. I wanted to map these to into a Dictionary collection. So that at the end the dictionary looks like this: ["LanguageName","IsoCode"].
private static Dictionary<string, string> languageToIsoCode; //dictionary cache
private void InitializeLanguageCacheDictionary()
{
using (var unitOfWork = dataAccessUnitOfWorkFactory.Create())
{
languageToIsoCode = (from p in unitOfWork.OwEntities.CTLANG
select new {p.LANGUAGENAME, p.ISOCODE}).ToDictionary(p => p.LANGUAGENAME, p => p.ISOCODE);
}
}
Thanks to #D.Petrov I also found a way to search for the key in a dictionary and give its value back.
And this is how I optimized my method to use the dictionary cache.
private string GetLanguageForIsoCode(string isoCode)
{
if (languageToIsoCode == null)//if cache empty initialize it
{
InitializeLanguageCacheDictionary();
}
//searches inside the dictionary, look for value and then return key
//might be bad if there are more than one value asigned to a key
//because value does not habe to be unique
string languageFromIsoCodeFromCache = languageToIsoCode.FirstOrDefault(item => item.Value == isoCode).Key;
if (languageFromIsoCodeFromCache == null)
{
//fallback and use the German language as default
return CultureInfo.GetCultureInfo("de").NativeName;
}
return languageFromIsoCodeFromCache;
}

Why do the members of my list get overwritten with the last member of said list?

I am trying to write a program that prints out (in a string variable) the following information about an mdb database:
Table Name
Total number of columns of the table
List of columns as follows:
Column Name:
Column Data Type:
To accomplish this I used two custom types (public classes) and of course, lists. Here is the code I have so far (which by the way has been adjusted not in small part thanks to questions and answers gathered here):
Here are the classes I created to define the two new types I am using:
public class ClmnInfo
{
public string strColumnName { get; set; }
public string strColumnType { get; set; }
}
public class TblInfo
{
public string strTableName { get; set; }
public int intColumnsQty { get; set; }
public List<ClmnInfo> ColumnList { get; set; }
}
Here is the code that actually gets the data. Keep in mind that I am using OleDB to connect to the actual data and everything works fine, except for the problem I will describe below.
As a sample, I am currently testing this code with a simple 1 table db, containing 12 columns of type string save for 1 int32 (Long Int in Access).
//Here I declare and Initialize all relevant variables and Lists
TblInfo CurrentTableInfo = new TblInfo();
ClmnInfo CurrentColumnInfo = new ClmnInfo();
List<TblInfo> AllTablesInfo = new List<TblInfo>();
//This loop iterates through each table obtained and imported previously in the program
int i = 0;
foreach (DataTable dt in dtImportedTables.Tables)
{
CurrentTableInfo.strTableName = Globals.tblSchemaTable.Rows[i][2].ToString(); //Gets the name of the current table
CurrentTableInfo.intColumnsQty = dt.Columns.Count; //Gets the total number of columns in the current table
CurrentTableInfo.ColumnList = new List<ClmnInfo>(); //Initializes the list which will house all of the columns
//This loop iterates through each column in the current table
foreach (DataColumn dc in dt.Columns)
{
CurrentColumnInfo.ColumnName = dc.ColumnName; // Gets the current column name
CurrentColumnInfo.ColumnType = dc.DataType.Name; // Gets the current column data type
CurrentTableInfo.ColumnList.Add(CurrentColumnInfo); // adds the information just obtained as a member of the columns list contained in CurrentColumnInfo
}
//BAD INSTRUCTION FOLLOWS:
AllTablesInfo.Add(CurrentTableInfo); //This SHOULD add The collection of column_names and column_types in a "master" list containing the table name, the number of columns, and the list of columns
}
I debugged the code and watched all variables. It works great (the table name and column quantity gets registered correctly, as well as the list of column_names, column_types for that table), but when the "bad" instruction gets executed, the contents of AllTablesInfo are not at all what they should be.
The table name is correct, as well as the number of columns, and the columns list even has 12 members as it should have, but each member of the list is the same, namely the LAST column of the database I am examining. Can anyone explain to me why CurrentTableInfo gets overwritten in this manner when it is added to the AllTablesInfo list?

You're creating a single TblInfo object, and then changing the properties on each iteration. Your list contains lots of references to the same object. Just move this line:
TblInfo CurrentTableInfo = new TblInfo();
to the inside of the first loop, and this line:
ClmnInfo CurrentColumnInfo = new ClmnInfo();
inside the nested foreach loop, so that you're creating new instances on each iteration.
Next:
Important
Make sure you understand why it was failing before. Read my article on references if you're not sure how objects and references (and value types) work in C#
Use camelCased names instead of CamelCased ones for local variables
Consider using an object initializer for the ClmnInfo
Change your type names to avoid unnecessary abbreviation (TableInfo, ColumnInfo)
Change your property names to avoid pseudo-Hungarian notation, and make them PascalCased
Consider rewriting the whole thing as a LINQ query (relatively advanced)
The pre-LINQ changes would leave your code looking something like this:
List<TableInfo> tables = new List<TableInfo>();
int i = 0;
foreach (DataTable dt in dtImportedTables.Tables)
{
TableInfo table = new TableInfo
{
Name = Globals.tblSchemaTable.Rows[i][2].ToString(),
// Do you really need this? Won't it be the same as Columns.Count?
ColumnCount = dt.Columns.Count,
Columns = new List<ColumnInfo>()
};
foreach (DataColumn dc in dt.Columns)
{
table.Columns.Add(new ColumnInfo {
Name = dc.ColumnName,
Type = dc.DataType.Name
});
}
tables.Add(table);
// I assume you meant to include this?
i++;
}
With LINQ:
List<TableInfo> tables =
dtImportedTables.Tables.Zip(Globals.tblSchemaTable.Rows.AsEnumerable(),
(table, schemaRow) => new TableInfo {
Name = schemaRow[2].ToString(),
// Again, only if you really need it
ColumnCount = table.Columns.Count,
Columns = table.Columns.Select(column => new ColumnInfo {
Name = column.ColumnName,
Type = column.DataType.Name
}).ToList()
}
}).ToList();

You have only created one instance of TblInfo.

It's because you only have a single instance of TblInfo, which you keep updating in your loop and then add another reference to it to the List. Thus your list has many references to the same object in memory.
Move the creation of the CurrentTableInfo instance inside the for loop.

Read row values with entities

I am creating a Pie Chart and its name-value pair are being retrieved from the database.
how to read the row details in order to get the values and store it one property ?
public override void OnApplyTemplate()
{
Ram.DataContext = new List<UsageRAM>()
{ new UsageRAM() { name = "Available" , value =/*how to get the value here*/ },
new UsageRAM() { name = "Used" , value =/*how to get the value here*/ }};
base.OnApplyTemplate();
}
public class UsageRAM
{
public string name { get; set; }
public double value { get; set; }
}
EDIT
--Answer which worked for me--
using (DB db = new DB())
{
var row = (from c in db.UsageRAMs
orderby c.UsageRamID descending
select c).First();
Ram.DataContext = new List<UsageRAM>()
{ new UsageRAM() { name = "Available" , value = row.Available},
new UsageRAM() { name = "Used" , value = row.Used }};

If you're using EF, simply add a new model to your project and include the requried table(s) in this model. Then you can use the newly created Entities object to read your db values as follows:
var Rows = context.YourTableName.Where(YourCondition).ToArray();
You can then iterate over the Rows collection using foreach or something.
If you need to read values from a single row, you may want to use First instead of Where above. That will return a single object whose properties will map to your db fields and can directly be assigned in the example code you posted in the question.
EXAMPLE
Say your model's Entity class is named MyEntities and it contains the table UsageRam, which has two fields Available and Used. Then it will take the following code:
using(MyEntities e = new MyEntities)
{
var Row = e.MyTable.First(x => x.UsageRamID = **[ID]**);
MessageBox.Show("Available=" + Row.Available.ToString() + ",Used=" + Row.Used.ToString();
}
I have just shown values in message box, you can assign them to anything you want.
Another Example
using(MyEntities e = new MyEntities)
{
var Rows = e.MyTable.Where(x => x.UsageRamID > 10 && x.UsageRamID < 20);
foreach(var Row in Rows)
MessageBox.Show("Available=" + Row.Available.ToString() + ",Used=" + Row.Used.ToString();
}
EXAMPLE 3
The code in your updated post appears fine to me, though I do have some doubts about the db design, but given your table is indexed on RamUsageID column, this should give you correct results without much performance impact. I generally prefer lambada expressions over query, so I'd rather write it like:
db.RamUsage.OrderByDescending(x => x.RamUsageID).First()