Dynamic LINQ Simple Query

Strongly typed LINQ versus Dynamic Linq

When querying data using Dynamic LINQ, everything can be expressed using strings. This includes predicates, selectors, and sorting.

Strongly typed LINQ looks like:

1: var result = context.Customers
2:     .Where(c => c.City == "Paris")
3:     .ToList();

Dynamic LINQ looks like:

1: var resultDynamic = context.Customers
2:     .Where("City == \"Paris\"")
3:     .ToList();

When we break down these examples:

1. The context.Customers in this case is a DbSet<Customer>, which implements IQueryable<T>. This is the same starting point for both examples.

2. The Where-predicate for Dynamic Linq is written as a string, where the same property is used (City) and the same value (Paris).

   Since the value "Paris" is a string itself, we need to escape the double quotes with a \. So the " becomes a \".

   This also is required for the escape character \ itself, so if you want to query on a string like "\r\n", you need to double escape the escape characters, so it becomes:

   .Where("Text == \"\\r\\n\"")
   

   For more examples, see this unit-test.

3. The ToList() method for both examples will just return a strongly typed list: List<Customer>.

Note that instead of using the query value directly in the string like "City == \"Paris\"" you can also use composite string formatting. But instead of using the format item syntax {n}, you need to use @n (Where n is the index). So line 2 in the example above will become:

.Where("City == @0", "Paris")`

And of course, it's not required to specify the value as a hard-coded value. So another valid Dynamic LINQ query example will be:

1: string cityToSearch = "Paris";
2: var resultDynamic = context.Customers
3:     .Where("City == @0", cityToSearch)
4:     .ToList();

View all above examples here

See chapters below for more basic query examples.

More Where examples

Note that it's also possible to query data using multiple predicates:

1: var result = context.Customers
2:     .Where(c => c.City == "Paris" && c.Age > 50)
3:     .ToList();

This code can be used when using Dynamic LINQ:

1: var resultDynamic = context.Customers
2:     .Where("City == \"Paris\" && Age > 50")
3:     .ToList();

Note that instead of the &&-operand, you can use and. Also in this example you can use composite string formatting. In that case, the Dynamic LINQ will be:

1: var resultDynamic = context.Customers
2:     .Where("City == @0 and Age > @1", "Paris", 50)
3:     .ToList();

You can also mimic the strongly typed Where-predicate using the => operator, like this:

1: var resultDynamic = context.Customers
2:     .Where("c => c.City == \"Paris\" && c.Age > 50")
3:     .ToList();

View all above examples here

Selecting entities and properties

Selecting entities or only the properties you need is another powerful feature of LINQ. Since the generated SQL will only return a limited set and not the whole entity, it is more useful if you only want to return a few columns.

Here is an example of a strongly typed:

1: var result = context.Customers
2:     .Select(c => new { c.City, c.CompanyName } )
3:     .ToList();

Dynamic LINQ looks like:

1: var resultDynamic = context.Customers
2:     .Select("new { City, CompanyName }")
3:     .ToDynamicList();

When we break down these two examples:

1. The context.Customers in this case is a DbSet<Customer>, which implements IQueryable<T>. This is the same starting point for both examples.
2. The Select-method for Dynamic Linq is written as a string, where the same properties are used (City and CompanyName).
3. For Dynamic LINQ we need to use the ToDynamicList() method, because the return from the Select is an IQueryable. The result from both the strongly typed and dynamic example is the same: a list from a dynamic-generated class with two properties (City and CompanyName).

View all above examples here

Ordering results

Sorting the result based on a property or multiple properties is another feature from LINQ. Observe the differences.

A strongly typed example to sort on City and then on CompanyName would look like:

1: var ordered = context.Customers
2:     .OrderBy(c => c.City).ThenBy(c => c.CompanyName)
3:     .ToList();

Dynamic LINQ looks like:

1: var orderedDynamic = context.Customers
2:     .OrderBy("City, CompanyName")
3:     .ToList();

When we break down these two examples:

1. The context.Customers in this case is a DbSet<Customer>, which implements IQueryable<T>. This is the same starting point for both examples.
2. In the strongly typed LINQ example, you need to call the OrderBy-method, followed by the ThenBy-method to sort the result; first on the City and then on the CompanyName. For Dynamic Linq you only need to use the OrderBy-method, and provide the two sort properties as a comma separated string.
3. The ToList() method for both examples will return a strongly typed list: List<Customer>.

Ordering results (combining ascending and descending)

In case you want to sort Descending, or a mixed combination, you can use the following Dynamic LINQ:

1: var orderedDynamic = context.Customers
2:     .OrderBy("City").ThenBy("CompanyName desc")
3:     .ToList();

Or

1: var orderedDynamic = context.Customers
2:     .OrderBy("City, CompanyName desc")
3:     .ToList();

The examples above will perform the sorting on the City property Ascending (= default) and then the sorting will be on the CompanyName in a Descending way.

View all above examples here