Entity Framework Dynamic Filters Filter

Description

Filter add a filter to a single entity. You can filter the query with a predicate to exclude certain data. Filter values can be provided in the following different ways:

• Specific Value
• Delegate Expressions
• Parameter Expressions
• LINQ Filters

Specific Value

Filters can be defined on a specific entity class or an interface by providing a specific value, e.g. an IsDeleted filter created on an ISoftDelete interface which will automatically filter those entities by applying the condition "IsDeleted==false".

modelBuilder.Filter("IsDeleted", (ISoftDelete d) => d.IsDeleted, false);

This filter will apply to all classes that implements ISoftDelete.

Delegate Expressions

Filter values can also be provided via a delegate/expression instead of a specific value which allows you to change the parameter value dynamically. For example, a filter can be created on the UserID and provided per HTTP request.

modelBuilder.Filter("Notes_CurrentUser", (Note n) => 
			n.PersonID, () => GetPersonIDFromPrincipal(Thread.CurrentPrincipal));

Each time the query is executed, this delegate will be evaluated to obtain the PersonID associated with each request.

Parameter Expressions

Parameter delegate expressions can be specified as either a Func < object > or a Func<DbContext, object>.

// Specified as Func<object>
modelBuilder.Filter("Notes_CurrentUser", (Note n) => 
			n.PersonID, () => GetPersonIDFromPrincipal(Thread.CurrentPrincipal));

// Specified as Func<DbContext, object>
modelBuilder.Filter("Notes_CurrentUser", (Note n) => 
			n.PersonID, (MyContext ctx) => ctx.CurrentPersonID);

In the latest declaration, the parameter value is set to the value of the CurrentPersonID property in the current DbContext instance.

LINQ Filters

Filters can also be created using linq conditions and with multiple parameters.

The following command creates a filter that limits BlogEntry records by AccountID and an IsDeleted flag.

modelBuilder.Filter("BlogEntryFilter", 
			(BlogEntry b, Guid accountID, bool isDeleted) => 
			(b.AccountID == accountID) && (b.IsDeleted == isDeleted), () => 
			GetPersonIDFromPrincipal(Thread.CurrentPrincipal), () => false);

A parameter is created for each condition with parameter names "accountID" and "isDeleted".

The LINQ syntax support the Contains() operator on Enumerable to generate SQL "in" clauses:

var values = new List<int> { 1, 2, 3, 4, 5 };
modelBuilder.Filter("ContainsTest", (BlogEntry b, List<int> valueList) => 
				valueList.Contains(b.IntValue.Value), () => values);