Analyze LINQ Expressions

Overview

LINQ is a query syntax included in the C# language. The .NET/C# driver can translate a subset of LINQ expressions into MongoDB aggregation pipelines.

To learn more about LINQ, see the following resources:

• LINQ in the .NET/C# driver documentation

• LINQ in the Microsoft C# guide

To learn more about aggregation pipelines, see Aggregation in the MongoDB manual.

Use the C# Analyzer to learn the following about your LINQ expressions:

• How your LINQ expressions translate into the MongoDB Query API

• If any of your LINQ expressions are not supported

Translate into the MongoDB Query API

Click the following tabs to see an example of a LINQ expression and its corresponding MongoDB Query API translation:

var books = queryableCollection
       .Where(b =>
           b.Genre == genre &&
           b.Price >= minPrice &&
           b.Title.Contains(titleSearchTerm))
       .OrderBy(b => b.Price)
       .ToList();

[{ "$match" : {
     "Genre" : genre,
     "Price" : { "$gte" : minPrice },
     "Title" : /titleSearchTerm/s }
  },
  { "$sort" : { "Price" : 1 } }]

Analyze LINQ in Visual Studio

To analyze your LINQ expressions in Visual Studio, perform the following actions:

1. Install the C# Analyzer as described in the Install guide.

2. Write a LINQ expression with the .NET/C# driver.

3. Move your mouse over the ... annotation beneath the first method of your LINQ expression to display an information message that contains the MongoDB Query API translation.

Simple LINQ Expressions

The C# Analyzer analyzes LINQ expressions in the following syntax types:

• Method syntax

• Query syntax

Click on the following corresponding tab to see a LINQ expression written in method syntax with or without an information message displayed:

Without Information Message

With Information Message

Click on the following corresponding tab to see a LINQ expression written in query syntax with or without an information message displayed:

Without Information Message

With Information Message

Unsupported LINQ Expressions

If your LINQ expression is not supported, the C# Analyzer outputs a NotSupportedLinqExpression warning.

Click the following tabs to see a code snippet containing an unsupported LINQ expression and the corresponding warning message displayed by the C# Analyzer:

Code Snippet

Warning

The following code snippet contains the unsupported GetHashCode LINQ expression:

var result = queryableColl.Where(b => b.GetHashCode() == 167);

The following screenshot shows the annotation displayed by the C# Analyzer underneath the preceding code snippet in Visual Studio:

The following is the warning generated by the C# Analyzer:

Expression not supported: b.GetHashCode().

The following screenshot shows the warning displayed in Visual Studio:

Tip

Error List Panel

If you are using Visual Studio for Windows, you can view the output from the {+product+-short} in the Error List window.

To learn more, see Error List Window from Microsoft.

To view more examples of unsupported LINQ expressions, see the MongoDB C# Analyzer Github repository.

var result = queryableColl.Where(b => b.Title.Substring(0) == "Pane");

Supported in LINQ3 only: db.coll.Aggregate([{ "$match" : { "$expr" : { "$eq" : [{ "$substrCP" : ["$Title", 0, { "$subtract" : [{ "$strLenCP" : "$Title" }, 0] }] }, "Pane"] } } }])