Convert to Lambda expression

Question

I am a newbie in lambda expression, can anyone help me on converting the line of codes into lambda expression. Please...it makes me pissed off.

var query =

 from c in

 (from line in File.ReadAllLines(filePath)

 let customerRecord = line.Split(',')

 select new Customer()

 Firstname = customerRecord[0],

 Lastname = customerRecord[1],

 JobTitle = customerRecord[2],

 City = customerRecord[3],

 Country = customerRecord[4]

})

Vulpes · Answer

To add multiple records to the database, I'd try the following: var profiles = (File.ReadAllLines(ConfigurationManager.AppSettings["employeefile"].ToString()) .Select(recordindex => recordindex.Split(',')) .Select(recordindex => new EmployeeProfile { employeeid = recordindex[0], lastname = recordindex[1], firstname = recordindex[2], middlename = recordindex[3], address = recordindex[4], gender = recordindex[5], civilstatus = recordindex[6], contacts = recordindex[7], })); using (var context = new DataAccess.Database()) { foreach(EmployeeProfile ep in profiles) { context.EmployeeProfile.Add(ep); } context.SaveChanges(); }

Vulpes · Answer

Well, the book that first helped me to get to grips with LINQ was this one for C# 3.0: http://www.amazon.com/3-0-Nutshell-Desktop-Reference-OReilly/dp/0596527578 But, there's a new edition just come out for the forthcoming C# 5.0: http://www.amazon.com/5-0-Nutshell-The-Definitive-Reference/dp/1449320104/ref=dp_ob_title_bk

boycoto · Answer

Thanks a lot Vulpes, you're such a genius. Any book or tutorial that you can suggest.

boycoto · Answer

The code is correct, but if I change to All(), it gives me an error. In my csv file, I am reading, 300 records of employeeprofile.

Vulpes · Answer

That looks like Entity Framework code but I'd imagine that you need to add an EmployeeProfile object in order to create a record in the database. I'm not sure how many EmployeeProfile objects your query will generate but to add the first one, I'd try: EmployeeProfile ep = (File.ReadAllLines(ConfigurationManager.AppSettings["employeefile"].ToString()) .Select(recordindex => recordindex.Split(',')) .Select(recordindex => new EmployeeProfile { employeeid = recordindex[0], lastname = recordindex[1], firstname = recordindex[2], middlename = recordindex[3], address = recordindex[4], gender = recordindex[5], civilstatus = recordindex[6], contacts = recordindex[7], })).First(); using (var context = new DataAccess.Database()) { context.EmployeeProfile.Add(ep); context.SaveChanges(); }

boycoto · Answer

Thank you Vulpes, now I have a clear understanding on the statements that I am doing. I have another problem, how am I able to insert the record into the table? Considering my code below, which I adapted from your given example Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable{mso-style-name:"Table Normal";mso-tstyle-rowband-size:0;mso-tstyle-colband-size:0;mso-style-noshow:yes;mso-style-priority:99;mso-style-qformat:yes;mso-style-parent:"";mso-padding-alt:0in 5.4pt 0in 5.4pt;mso-para-margin-top:0in;mso-para-margin-right:0in;mso-para-margin-bottom:10.0pt;mso-para-margin-left:0in;line-height:115%;mso-pagination:widow-orphan;font-size:11.0pt;font-family:"Calibri","sans-serif";mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:"Times New Roman";mso-fareast-theme-font:minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;} string employeeData = (File.ReadAllLines(ConfigurationManager.AppSettings["employeefile"].ToString()) .Select(recordindex => recordindex.Split(',')) .Select(recordindex => new EmployeeProfile { employeeid = recordindex[0], lastname = recordindex[1], firstname = recordindex[2], middlename = recordindex[3], address = recordindex[4], gender = recordindex[5], civilstatus = recordindex[6], contacts = recordindex[7], })).ToString(); using (var context = new DataAccess.Database()) { context.EmployeeProfile.Add(EmployeeProfile); context.SaveChanges(); } using the class employeeprofile it gives me EmployeeProfile Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable{mso-style-name:"Table Normal";mso-tstyle-rowband-size:0;mso-tstyle-colband-size:0;mso-style-noshow:yes;mso-style-priority:99;mso-style-qformat:yes;mso-style-parent:"";mso-padding-alt:0in 5.4pt 0in 5.4pt;mso-para-margin-top:0in;mso-para-margin-right:0in;mso-para-margin-bottom:10.0pt;mso-para-margin-left:0in;line-height:115%;mso-pagination:widow-orphan;font-size:11.0pt;font-family:"Calibri","sans-serif";mso-ascii-font-family:Calibri;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:"Times New Roman";mso-fareast-theme-font:minor-fareast;mso-hansi-font-family:Calibri;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi;} is a 'type' but is used like a 'variable', so how I am able to deal with it.

Vulpes · Answer

You need to distinguish between LINQ (language integrated query) and lambda expressions (anonymous methods). LINQ queries can actually be written using two kinds of syntax: 1. The form you used in your original post which uses special C# keywords such as from, where, let, select etc. This kind is known as 'query expressions' and is popular with folks who do a lot of database work because of its superficial resemblance to SQL. 2. The form you used in your latest post which uses extension methods such as Select, Where, OrderBy etc which can all be chained together. This kind is known as 'fluent syntax' and is popular with folks who know functional programming languages such as F# and Haskell or don't care much for SQL. It's also possible to combine the two types of syntax which Jignesh did in his post by applying the Skip extension method to the result of a query expression. Lambda expressions are a flexible form of anonymous method, which use syntax inspired by functional languages and which can be comverted automatically to compatible delegates. They are indispensible when you use the second type of LINQ syntax because the extension methods nearly always require delegates to be passed to them as parameters and an easy way to pass a delegate is to use a lambda expression. So, for example, the following is a lambda expression: x => x.Split(',') which takes a parameter x of type string and returns a string array which is the result of splitting x using a comma as a separator. The compiler infers that 'x' is a string because File.ReadAllLines("Employees.csv") generates a sequence of strings to which the Select extension method is applied. This is also a lambda expression: x => new EmployeeObject { FirstName=x[0], LastName=x[1], DateOfBirth=DateTime.Parse(x[2]), Department=x[3] } which takes a parameter of type string[] and returns an 'anonymous type' which has four properties : FirstName, LastName, DateOfBirth and Department. Again the compiler infers that x is a string[] because the result of the previous operation (splitting each line in the file) generates a sequence of string[]'s. So, to answer, your original question the result of expressing your query expression in fluent syntax would be: var query = File.ReadAllLines(filePath). Select(x => line.Split(',')). Select(x => new Customer { Firstname = x[0], Lastname = x[1], JobTitle = x[2], City = x[3], Country = x[4] });

boycoto · Answer

I found this code on the web, but I have no idea it was coded, the intellisense does not display something like .Select. File.ReadAllLines("Employees.csv") .Select(x => x.Split(',')) .Select(x => new EmployeeObject { FirstName=x[0], LastName=x[1], DateOfBirth=DateTime.Parse(x[2]), Department=x[3] });

boycoto · Answer

does the code that I posted was already on its lambda expression?

Jignesh Trivedi · Answer

hi, I think you try to read csv file. if yes so you must skip first record which is header. try... var query = (from line in File.ReadAllLines(@"E:\JTtest.txt") let customerRecord = line.Split(',') select new Customer() { Firstname = customerRecord[0], Lastname = customerRecord[1], JobTitle = customerRecord[2], City = customerRecord[3], Country = customerRecord[4] }).Skip(1); it store the record without header... hope this will help you.

Convert to Lambda expression

Insert Link

Embed YouTube Video

Table Options

Insert Image

Answers (10)