Generate a C# expression that can concatenate two strings together

I'm trying to concatenate two strings together in a dynamic linq expression. The parameter I pass to the function must be a Dictionary<string, object>. The problem is that The Expression.Add throws me an error because it doesn't know how to add strings.

What I'm trying to achieve:

x => (string)x["FirstName"] + " Something here..."

What I have:

var pe = Expression.Parameter(typeof(Dictionary<string, object>), "x");

var firstName = Expression.Call(pe, typeof(Dictionary<string, object>).GetMethod("get_Item"), Expression.Constant("FirstName"));

var prop = Expression.Convert(firstName, typeof(string));

var exp = Expression.Add(prop, Expression.Constant(" Something here..."))

edited Nov 26 '18 at 2:11

Cœur

18.7k9110150

asked Feb 2 '17 at 2:05

Andoni Zubizarreta

4241415

Does your Dictionary<string,object> has FirstName as a string? {Key:"FirstName",Value:"Andoni"}?

– Vijay
Feb 2 '17 at 2:18

add a comment |

What I'm trying to achieve:

x => (string)x["FirstName"] + " Something here..."

What I have:

var pe = Expression.Parameter(typeof(Dictionary<string, object>), "x");

var firstName = Expression.Call(pe, typeof(Dictionary<string, object>).GetMethod("get_Item"), Expression.Constant("FirstName"));

var prop = Expression.Convert(firstName, typeof(string));

var exp = Expression.Add(prop, Expression.Constant(" Something here..."))

edited Nov 26 '18 at 2:11

Cœur

18.7k9110150

asked Feb 2 '17 at 2:05

Andoni Zubizarreta

4241415

Does your Dictionary<string,object> has FirstName as a string? {Key:"FirstName",Value:"Andoni"}?

– Vijay
Feb 2 '17 at 2:18

add a comment |

What I'm trying to achieve:

x => (string)x["FirstName"] + " Something here..."

What I have:

var pe = Expression.Parameter(typeof(Dictionary<string, object>), "x");

var firstName = Expression.Call(pe, typeof(Dictionary<string, object>).GetMethod("get_Item"), Expression.Constant("FirstName"));

var prop = Expression.Convert(firstName, typeof(string));

var exp = Expression.Add(prop, Expression.Constant(" Something here..."))

edited Nov 26 '18 at 2:11

Cœur

18.7k9110150

asked Feb 2 '17 at 2:05

Andoni Zubizarreta

4241415

What I'm trying to achieve:

x => (string)x["FirstName"] + " Something here..."

What I have:

var pe = Expression.Parameter(typeof(Dictionary<string, object>), "x");

var firstName = Expression.Call(pe, typeof(Dictionary<string, object>).GetMethod("get_Item"), Expression.Constant("FirstName"));

var prop = Expression.Convert(firstName, typeof(string));

var exp = Expression.Add(prop, Expression.Constant(" Something here..."))

c# linq lambda asp.net-core

edited Nov 26 '18 at 2:11

Cœur

18.7k9110150

asked Feb 2 '17 at 2:05

Andoni Zubizarreta

4241415

edited Nov 26 '18 at 2:11

Cœur

18.7k9110150

asked Feb 2 '17 at 2:05

Andoni Zubizarreta

4241415

edited Nov 26 '18 at 2:11

Cœur

18.7k9110150

edited Nov 26 '18 at 2:11

Cœur

18.7k9110150

edited Nov 26 '18 at 2:11

Cœur

18.7k9110150

asked Feb 2 '17 at 2:05

Andoni Zubizarreta

4241415

asked Feb 2 '17 at 2:05

Andoni Zubizarreta

4241415

asked Feb 2 '17 at 2:05

Andoni Zubizarreta

4241415

Does your Dictionary<string,object> has FirstName as a string? {Key:"FirstName",Value:"Andoni"}?

– Vijay
Feb 2 '17 at 2:18

add a comment |

Does your Dictionary<string,object> has FirstName as a string? {Key:"FirstName",Value:"Andoni"}?

– Vijay
Feb 2 '17 at 2:18

Does your Dictionary<string,object> has FirstName as a string? {Key:"FirstName",Value:"Andoni"}?

– Vijay
Feb 2 '17 at 2:18

add a comment |

2 Answers
2

active

oldest

votes

Adding strings is neither one of the types that expressions handles explicitly (as it does for numeric primitives) nor going to work due to an overload of + (since string has no such overload), so you need to explicitly defined the method that should be called when overloading:

Expression.Add(

  prop,

  Expression.Constant(" Something here...")

  typeof(string).GetMethod("Concat", new {typeof(string), typeof(string)}))

This makes the overload of string.Concat that takes two string arguments the method used.

You could also use Expresssion.Call but this keeps your + intention explicit (and is what the C# compiler does when producing expressions, for that reason).

answered Feb 2 '17 at 3:00

Jon Hanna

91.3k9111206

add a comment |

Adding and concatenating are completely different processes. When you "add" two strings together, you are concatenating them, since doing a mathematical addition on strings makes no sense.

The best way to concatenate strings is by using String.Concat. You can use Expression.Call to generate the method expression:

// Create the parameter expressions

var strA = Expression.Parameter(typeof(string));

var strB = Expression.Parameter(typeof(string));



// Create a method expression for String.Join

var methodInfo = typeof(string).GetMethod("Concat", new { typeof(string), typeof(string) });

var join = Expression.Call(methodInfo, strA, strB);

edited Feb 2 '17 at 6:51

answered Feb 2 '17 at 2:44

Abion47

6,60821739

@Rob Fair point, will edit.

– Abion47
Feb 2 '17 at 2:46

String.Join is different from concatenating strings. String.Join(a, b) will yield b.

– Rob♦
Feb 2 '17 at 2:46

@Rob I'm figuring out the code for using String.Concat instead of String.Join, but I do feel like pointing out that Join and Concat aren't that different. Join just concatenates an array of strings together separated by a given delimiter, which can be an empty string. String.Join("", "a", "b") will return "ab".

– Abion47
Feb 2 '17 at 2:50

@Rob So while my current code isn't optimal, it's still entirely usable.

– Abion47
Feb 2 '17 at 2:51

2

If it's not the best way, then you shouldn't say it's the best way.

– Jon Hanna
Feb 2 '17 at 2:55

|
show 4 more comments

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

Expression.Add(

  prop,

  Expression.Constant(" Something here...")

  typeof(string).GetMethod("Concat", new {typeof(string), typeof(string)}))

This makes the overload of string.Concat that takes two string arguments the method used.

You could also use Expresssion.Call but this keeps your + intention explicit (and is what the C# compiler does when producing expressions, for that reason).

answered Feb 2 '17 at 3:00

Jon Hanna

91.3k9111206

add a comment |

Expression.Add(

  prop,

  Expression.Constant(" Something here...")

  typeof(string).GetMethod("Concat", new {typeof(string), typeof(string)}))

This makes the overload of string.Concat that takes two string arguments the method used.

You could also use Expresssion.Call but this keeps your + intention explicit (and is what the C# compiler does when producing expressions, for that reason).

answered Feb 2 '17 at 3:00

Jon Hanna

91.3k9111206

add a comment |

Expression.Add(

  prop,

  Expression.Constant(" Something here...")

  typeof(string).GetMethod("Concat", new {typeof(string), typeof(string)}))

This makes the overload of string.Concat that takes two string arguments the method used.

You could also use Expresssion.Call but this keeps your + intention explicit (and is what the C# compiler does when producing expressions, for that reason).

answered Feb 2 '17 at 3:00

Jon Hanna

91.3k9111206

Expression.Add(

  prop,

  Expression.Constant(" Something here...")

  typeof(string).GetMethod("Concat", new {typeof(string), typeof(string)}))

This makes the overload of string.Concat that takes two string arguments the method used.

You could also use Expresssion.Call but this keeps your + intention explicit (and is what the C# compiler does when producing expressions, for that reason).

answered Feb 2 '17 at 3:00

Jon Hanna

91.3k9111206

answered Feb 2 '17 at 3:00

Jon Hanna

91.3k9111206

answered Feb 2 '17 at 3:00

Jon Hanna

91.3k9111206

answered Feb 2 '17 at 3:00

Jon Hanna

91.3k9111206

add a comment |

Adding and concatenating are completely different processes. When you "add" two strings together, you are concatenating them, since doing a mathematical addition on strings makes no sense.

The best way to concatenate strings is by using String.Concat. You can use Expression.Call to generate the method expression:

// Create the parameter expressions

var strA = Expression.Parameter(typeof(string));

var strB = Expression.Parameter(typeof(string));



// Create a method expression for String.Join

var methodInfo = typeof(string).GetMethod("Concat", new { typeof(string), typeof(string) });

var join = Expression.Call(methodInfo, strA, strB);

edited Feb 2 '17 at 6:51

answered Feb 2 '17 at 2:44

Abion47

6,60821739

@Rob Fair point, will edit.

– Abion47
Feb 2 '17 at 2:46

String.Join is different from concatenating strings. String.Join(a, b) will yield b.

– Rob♦
Feb 2 '17 at 2:46

@Rob I'm figuring out the code for using String.Concat instead of String.Join, but I do feel like pointing out that Join and Concat aren't that different. Join just concatenates an array of strings together separated by a given delimiter, which can be an empty string. String.Join("", "a", "b") will return "ab".

– Abion47
Feb 2 '17 at 2:50

@Rob So while my current code isn't optimal, it's still entirely usable.

– Abion47
Feb 2 '17 at 2:51

2

If it's not the best way, then you shouldn't say it's the best way.

– Jon Hanna
Feb 2 '17 at 2:55

|
show 4 more comments

Adding and concatenating are completely different processes. When you "add" two strings together, you are concatenating them, since doing a mathematical addition on strings makes no sense.

The best way to concatenate strings is by using String.Concat. You can use Expression.Call to generate the method expression:

// Create the parameter expressions

var strA = Expression.Parameter(typeof(string));

var strB = Expression.Parameter(typeof(string));



// Create a method expression for String.Join

var methodInfo = typeof(string).GetMethod("Concat", new { typeof(string), typeof(string) });

var join = Expression.Call(methodInfo, strA, strB);

edited Feb 2 '17 at 6:51

answered Feb 2 '17 at 2:44

Abion47

6,60821739

@Rob Fair point, will edit.

– Abion47
Feb 2 '17 at 2:46

String.Join is different from concatenating strings. String.Join(a, b) will yield b.

– Rob♦
Feb 2 '17 at 2:46

@Rob I'm figuring out the code for using String.Concat instead of String.Join, but I do feel like pointing out that Join and Concat aren't that different. Join just concatenates an array of strings together separated by a given delimiter, which can be an empty string. String.Join("", "a", "b") will return "ab".

– Abion47
Feb 2 '17 at 2:50

@Rob So while my current code isn't optimal, it's still entirely usable.

– Abion47
Feb 2 '17 at 2:51

2

If it's not the best way, then you shouldn't say it's the best way.

– Jon Hanna
Feb 2 '17 at 2:55

|
show 4 more comments

Adding and concatenating are completely different processes. When you "add" two strings together, you are concatenating them, since doing a mathematical addition on strings makes no sense.

The best way to concatenate strings is by using String.Concat. You can use Expression.Call to generate the method expression:

// Create the parameter expressions

var strA = Expression.Parameter(typeof(string));

var strB = Expression.Parameter(typeof(string));



// Create a method expression for String.Join

var methodInfo = typeof(string).GetMethod("Concat", new { typeof(string), typeof(string) });

var join = Expression.Call(methodInfo, strA, strB);

edited Feb 2 '17 at 6:51

answered Feb 2 '17 at 2:44

Abion47

6,60821739

Adding and concatenating are completely different processes. When you "add" two strings together, you are concatenating them, since doing a mathematical addition on strings makes no sense.

The best way to concatenate strings is by using String.Concat. You can use Expression.Call to generate the method expression:

// Create the parameter expressions

var strA = Expression.Parameter(typeof(string));

var strB = Expression.Parameter(typeof(string));



// Create a method expression for String.Join

var methodInfo = typeof(string).GetMethod("Concat", new { typeof(string), typeof(string) });

var join = Expression.Call(methodInfo, strA, strB);

edited Feb 2 '17 at 6:51

answered Feb 2 '17 at 2:44

Abion47

6,60821739

edited Feb 2 '17 at 6:51

answered Feb 2 '17 at 2:44

Abion47

6,60821739

answered Feb 2 '17 at 2:44

Abion47

6,60821739

answered Feb 2 '17 at 2:44

Abion47

6,60821739

@Rob Fair point, will edit.

– Abion47
Feb 2 '17 at 2:46

String.Join is different from concatenating strings. String.Join(a, b) will yield b.

– Rob♦
Feb 2 '17 at 2:46

@Rob I'm figuring out the code for using String.Concat instead of String.Join, but I do feel like pointing out that Join and Concat aren't that different. Join just concatenates an array of strings together separated by a given delimiter, which can be an empty string. String.Join("", "a", "b") will return "ab".

– Abion47
Feb 2 '17 at 2:50

@Rob So while my current code isn't optimal, it's still entirely usable.

– Abion47
Feb 2 '17 at 2:51

2

If it's not the best way, then you shouldn't say it's the best way.

– Jon Hanna
Feb 2 '17 at 2:55

|
show 4 more comments

@Rob Fair point, will edit.

– Abion47
Feb 2 '17 at 2:46

String.Join is different from concatenating strings. String.Join(a, b) will yield b.

– Rob♦
Feb 2 '17 at 2:46

@Rob I'm figuring out the code for using String.Concat instead of String.Join, but I do feel like pointing out that Join and Concat aren't that different. Join just concatenates an array of strings together separated by a given delimiter, which can be an empty string. String.Join("", "a", "b") will return "ab".

– Abion47
Feb 2 '17 at 2:50

@Rob So while my current code isn't optimal, it's still entirely usable.

– Abion47
Feb 2 '17 at 2:51

2

If it's not the best way, then you shouldn't say it's the best way.

– Jon Hanna
Feb 2 '17 at 2:55

@Rob Fair point, will edit.

– Abion47
Feb 2 '17 at 2:46

String.Join is different from concatenating strings. String.Join(a, b) will yield b.

– Rob♦
Feb 2 '17 at 2:46

@Rob I'm figuring out the code for using String.Concat instead of String.Join, but I do feel like pointing out that Join and Concat aren't that different. Join just concatenates an array of strings together separated by a given delimiter, which can be an empty string. String.Join("", "a", "b") will return "ab".

– Abion47
Feb 2 '17 at 2:50

@Rob So while my current code isn't optimal, it's still entirely usable.

– Abion47
Feb 2 '17 at 2:51

If it's not the best way, then you shouldn't say it's the best way.

– Jon Hanna
Feb 2 '17 at 2:55

|
show 4 more comments

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