Question

我希望能够允许指定可选参数，因此我可以重载 Accumulate()方法，是否可以完成？ < / p>

我想重载以允许指定分隔符，我已经看到其他人必须强制指定分隔符，但这种行为不合适。

CREATE AGGREGATE dbo.Concatenate (@input nvarchar(max), <OPTIONAL PARAMETER HERE>)
RETURNS nvarchar(max)

作为参考，这里是包含我想要重载的Accumulate()方法的聚合类代码：

using System;
using System.Data;
using Microsoft.SqlServer.Server;
using System.Data.SqlTypes;
using System.IO;
using System.Text;


namespace CLR.Utilities {
    /// <summary>
    /// <list type="references">
    ///     <reference>
    ///         <name>How to: Create and Run a CLR SQL Server Aggregate</name>
    ///         <link>http://msdn.microsoft.com/en-us/library/91e6taax(v=vs.90).aspx</link>
    ///     </reference>
    ///     <reference>
    ///         <name>SqlUserDefinedAggregateAttribute</name>
    ///         <link>http://msdn.microsoft.com/en-us/library/microsoft.sqlserver.server.sqluserdefinedaggregateattribute(v=vs.90).aspx</link>
    ///     </reference>
    ///     <reference>
    ///         <name>Invoking CLR User-Defined Aggregate Functions (Provides seed code for this function)</name>
    ///         <link>http://technet.microsoft.com/en-us/library/ms131056.aspx</link>
    ///     </reference>
    /// </list>
    /// </summary>
    [Serializable]
    [SqlUserDefinedAggregate(
        Format.UserDefined,                 //use clr serialization to serialize the intermediate result
        IsInvariantToNulls = true,          //optimizer property
        IsInvariantToDuplicates = false,    //optimizer property
        IsInvariantToOrder = false,         //optimizer property
        MaxByteSize = -1)                   //no maximum size in bytes of persisted value
    ]
    public class Concatenate : IBinarySerialize {
        /// <summary>
        /// The variable that holds the intermediate result of the concatenation
        /// </summary>
        private StringBuilder intermediateResult;

        /// <summary>
        /// Initialize the internal data structures
        /// </summary>
        public void Init() {
            this.intermediateResult = new StringBuilder();
        }

        /// <summary>
        /// Accumulate the next value, not if the value is null
        /// </summary>
        /// <param name="value"></param>
        public void Accumulate([SqlFacet(MaxSize = -1)] SqlString value) {
            if (value.IsNull) {
                return;
            }

            this.intermediateResult.Append(value.Value.Trim()).Append(',');
        }

        /// <summary>
        /// Merge the partially computed aggregate with this aggregate.
        /// </summary>
        /// <param name="other"></param>
        public void Merge(Concatenate other) {
            this.intermediateResult.Append(other.intermediateResult);
        }

        /// <summary>
        /// Called at the end of aggregation, to return the results of the aggregation.
        /// </summary>
        /// <returns></returns>
        [return: SqlFacet(MaxSize = -1)]
        public SqlString Terminate() {
            string output = string.Empty;
            //delete the trailing comma, if any
            if (this.intermediateResult != null
                && this.intermediateResult.Length > 0) {
                output = this.intermediateResult.ToString(0, this.intermediateResult.Length - 1).Trim();
            }

            return new SqlString(output);
        }

        public void Read(BinaryReader r) {
            intermediateResult = new StringBuilder(r.ReadString());
        }

        public void Write(BinaryWriter w) {
            w.Write(this.intermediateResult.ToString().Trim());
        }
    }
}

如果可以设置可选参数，这里是我想要修改的部署代码：

IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[Concatenate]') AND type = N'AF')
DROP AGGREGATE [dbo].[Concatenate]
GO

IF  EXISTS (SELECT * FROM sys.assemblies asms WHERE asms.name = N'CLR.Utilities' and is_user_defined = 1)
DROP ASSEMBLY [CLR.Utilities]
GO

ALTER DATABASE [DatabaseName] SET TRUSTWORTHY ON
GO

CREATE ASSEMBLY [CLR.Utilities] FROM 'C:\Path\To\File\CLR.Utilities.dll' WITH PERMISSION_SET = UNSAFE
GO

CREATE AGGREGATE [dbo].[Concatenate] (@input nvarchar(max)) RETURNS nvarchar(max)
EXTERNAL NAME [CLR.Utilities].[CLR.Utilities.Concatenate]
GO

GRANT EXECUTE ON [dbo].[Concatenate] TO PUBLIC
GO

Answer 1

据我所知，无法使用可选参数制作clr函数或聚合，这很难过。

Answer 2

但是，您可以使参数成为必需参数，但可选择为null。并且，在您的C＃代码测试中，该值是否为null并相应地执行操作。类似的东西：

public void Accumulate([SqlFacet(MaxSize = -1)] SqlString value, SqlString delimiter) {
        string _delimiter;
        if (value.IsNull) {
            return;
        }

        if (delimiter.IsNull) {
            _delimiter = string.Empty;
        }
        else {
            _delimiter = Delimiter.Value;
        }

        this.intermediateResult.Append(value.Value.Trim()).Append(_delimiter);
    }

T-SQL CLR：你能用可选参数创建AGGREGATE吗？

2 个答案: