Table of Contents

Class PreconditionAttribute

Namespace
Discord.Commands
Assembly
Discord.Net.Commands.dll

Requires the module or class to pass the specified precondition before execution can begin.

[AttributeUsage(AttributeTargets.Class|AttributeTargets.Method, AllowMultiple = true, Inherited = true)]
public abstract class PreconditionAttribute : Attribute
Inheritance
PreconditionAttribute
Derived
Inherited Members

Examples

The following example creates a precondition to see if the user has sufficient role required to access the command.

public class RequireRoleAttribute : PreconditionAttribute
{
    private readonly ulong _roleId;

    public RequireRoleAttribute(ulong roleId)
    {
        _roleId = roleId;
    }

    public override async Task<PreconditionResult> CheckPermissionsAsync(ICommandContext context,
        CommandInfo command, IServiceProvider services)
    {
        var guildUser = context.User as IGuildUser;
        if (guildUser == null)
            return PreconditionResult.FromError("This command cannot be executed outside of a guild.");

        var guild = guildUser.Guild;
        if (guild.Roles.All(r => r.Id != _roleId))
            return PreconditionResult.FromError(
                $"The guild does not have the role ({_roleId}) required to access this command.");

        return guildUser.RoleIds.Any(rId => rId == _roleId)
            ? PreconditionResult.FromSuccess()
            : PreconditionResult.FromError("You do not have the sufficient role required to access this command.");
    }
}

Remarks

This precondition attribute can be applied on module-level or method-level for a command.

A "precondition" in the command system is used to determine if a condition is met before entering the command task. Using a precondition may aid in keeping a well-organized command logic.

The most common use case being whether a user has sufficient permission to execute the command.

Properties

ErrorMessage

When overridden in a derived class, uses the supplied string as the error message if the precondition doesn't pass. Setting this for a class that doesn't override this property is a no-op.

public virtual string ErrorMessage { get; set; }

Property Value

string

Group

Specifies a group that this precondition belongs to.

public string Group { get; set; }

Property Value

string

Remarks

Preconditions of the same group require only one of the preconditions to pass in order to be successful (A || B). Specifying Group = null or not at all will require all preconditions to pass, just like normal (A && B).

Methods

CheckPermissionsAsync(ICommandContext, CommandInfo, IServiceProvider)

Checks if the command has the sufficient permission to be executed.

public abstract Task<PreconditionResult> CheckPermissionsAsync(ICommandContext context, CommandInfo command, IServiceProvider services)

Parameters

context ICommandContext

The context of the command.

command CommandInfo

The command being executed.

services IServiceProvider

The service collection used for dependency injection.

Returns

Task<PreconditionResult>

See Also

ParameterPreconditionAttribute
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