2008年（8065）
分类： 服务器与存储
2008-04-21 12:53:35
Array Binding
The array bind feature enables applications to bind arrays of a type using the OracleParameter class. Using the array bind feature, an application can insert multiple rows into a table in a single database round-trip.
The following example inserts three rows into the Dept table with a single database round-trip. The OracleCommand ArrayBindCount property defines the number of elements of the array to use when executing the statement.
// C#
using System;
using System.Data;
using Oracle.DataAccess.Client;
class ArrayBindSample
{
static void Main()
{
OracleConnection con = new OracleConnection();
con.ConnectionString = "User Id=scott;Password=tiger;Data Source=oracle;";
con.Open();
Console.WriteLine("Connected successfully");
int[] myArrayDeptNo = new int[3] { 10, 20, 30 };
OracleCommand cmd = new OracleCommand();
// Set the command text on an OracleCommand object
cmd.CommandText = "insert into dept(deptno) values (:deptno)";
cmd.Connection = con;
// Set the ArrayBindCount to indicate the number of values
cmd.ArrayBindCount = 3;
// Create a parameter for the array operations
OracleParameter prm = new OracleParameter("deptno", OracleDbType.Int32);
prm.Direction = ParameterDirection.Input;
prm.Value = myArrayDeptNo;
// Add the parameter to the parameter collection
cmd.Parameters.Add(prm);
// Execute the command
cmd.ExecuteNonQuery();
Console.WriteLine("Insert Completed Successfully");
// Close and Dispose OracleConnection object
con.Close();
con.Dispose();
}
}
See Also:
"Value" for more information
OracleParameter Array Bind Properties
The OracleParameter class provides two properties for granular control when using the array bind feature:
ArrayBindSize
The ArrayBindSize property is an array of integers specifying the maximum size for each corresponding value in an array. The ArrayBindSize property is similar to the Size property of an OracleParameter object, except the ArrayBindSize property specifies the size for each value in an array.
Before the execution, the application must populate the ArrayBindSize property; after the execution, ODP.NET populates it.
The ArrayBindSize property is used only for parameter types that have variable length such as Clob, Blob, and Varchar2. The size is represented in bytes for binary datatypes, and characters for the Unicode string types. The count for string types does not include the terminating character. The size is inferred from the actual size of the value, if it is not explicitly set. For an output parameter, the size of each value is set by ODP.NET. The ArrayBindSize property is ignored for fixed-length datatypes.
ArrayBindStatus
The ArrayBindStatus property is an array of OracleParameterStatus values that specify the status of each corresponding value in an array for a parameter. This property is similar to the Status property of the OracleParameter object, except that the ArrayBindStatus property specifies the status for each array value.
Before the execution, the application must populate the ArrayBindStatus property. After the execution, ODP.NET populates the property. Before the execution, an application using the ArrayBindStatus property can specify a NULL value for the corresponding element in the array for a parameter. After the execution, ODP.NET populates the ArrayBindStatus property, indicating whether the corresponding element in the array has a null value, or if data truncation occurred when the value was fetched.
Error Handling for Array Binding
If an error occurs during an array bind execution, it can be difficult to determine which element in the Value property caused the error. ODP.NET provides a way to determine the row where the error occurred, making it easier to find the element in the row that caused the error.
When an OracleException object is thrown during an array bind execution, the OracleErrorCollection object contains one or more OracleError objects. Each of these OracleError objects represents an individual error that occurred during the execution, and contains a provider-specific property, ArrayBindIndex, which indicates the row number at which the error occurred.
The following example demonstrates error handling for array binding:
/* Database Setup
connect scott/tiger@oracle
drop table depttest;
create table depttest(deptno number(2));
*/
// C#
using System;
using System.Data;
using Oracle.DataAccess.Client;
class ArrayBindExceptionSample
{
static void Main()
{
OracleConnection con = new OracleConnection();
con.ConnectionString = "User Id=scott;Password=tiger;Data Source=oracle;";
con.Open();
OracleCommand cmd = new OracleCommand();
// Start a transaction
OracleTransaction txn = con.BeginTransaction(IsolationLevel.ReadCommitted);
try
{
int[] myArrayDeptNo = new int[3] { 10, 200000, 30 };
// int[] myArrayDeptNo = new int[3]{ 10,20,30};
// Set the command text on an OracleCommand object
cmd.CommandText = "insert into depttest(deptno) values (:deptno)";
cmd.Connection = con;
// Set the ArrayBindCount to indicate the number of values
cmd.ArrayBindCount = 3;
// Create a parameter for the array operations
OracleParameter prm = new OracleParameter("deptno", OracleDbType.Int32);
prm.Direction = ParameterDirection.Input;
prm.Value = myArrayDeptNo;
// Add the parameter to the parameter collection
cmd.Parameters.Add(prm);
// Execute the command
cmd.ExecuteNonQuery();
}
catch (OracleException e)
{
Console.WriteLine("OracleException {0} occured", e.Message);
if (e.Number == 24381)
for (int i = 0; i < e.Errors.Count; i++)
Console.WriteLine("Array Bind Error {0} occured at Row Number {1}",
e.Errors[i].Message, e.Errors[i].ArrayBindIndex);
txn.Commit();
}
cmd.Parameters.Clear();
cmd.CommandText = "select count(*) from depttest";
decimal rows = (decimal)cmd.ExecuteScalar();
Console.WriteLine("{0} row have been inserted", rows);
con.Close();
con.Dispose();
}
}
See Also:
"ArrayBindIndex" for more information
OracleParameterStatus Enumeration Types
Table: OracleParameterStatus Members lists OracleParameterStatus enumeration values.
OracleParameterStatus Members
Member Names
Description
Success
For input parameters, indicates that the input value has been assigned to the column.
For output parameters, indicates that the provider assigned an intact value to the parameter.
NullFetched
Indicates that a NULL value has been fetched from a column or an OUT parameter.
NullInsert
Indicates that a NULL value is to be inserted into a column.
Truncation
Indicates that truncation has occurred when fetching the data from the column.
Statement Caching
Statement caching eliminates the need to parse each SQL or PL/SQL statement before execution by caching server cursors created during the initial statement execution. Subsequent executions of the same statement can reuse the parsed information from the cursor, and then execute the statement without reparsing, for better performance.
In order to see performance gains from statement caching, Oracle recommends caching only those statements that will be repeatedly executed. Furthermore, SQL or PL/SQL statements should use parameters rather than literal values. Doing so takes full advantage of statement caching, because parsed information from parameterized statements can be reused even if the parameter values change in subsequent executions. However, if the literal values in the statements are different, the parsed information cannot be reused unless the subsequent statements also have the same literal values.
Statement Caching Connection String Attributes
The following connection string attributes control the behavior of the ODP.NET statement caching feature:
Statement Cache Size
This attribute enables or disables ODP.NET statement caching. By default, this attribute is set to 0 (disabled). If it is set to a value greater than 0, ODP.NET statement caching is enabled and the value specifies the maximum number of statements that can be cached for a connection. Once a connection has cached up to the specified maximum cache size, the cursor least recently used is freed to make room to cache the newly created cursor.
Statement Cache Purge
This attribute provides a way for connections to purge all statements that are cached when a connection is closed or placed back into the connection pool. By default, this attribute is set to false, which means that cursors are not freed when connections are placed back into the pool.
Enabling Statement Caching through the Registry
To enable statement caching by default for all ODP.NET applications running in a system, without changing the application, set the registry key of HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\HOMEID\ODP.NET\StatementCacheSize to a value greater than 0. (ID is the appropriate Oracle Home ID.) This value specifies the number of cursors that are to be cached on the server. By default, it is set to 0.
Statement Caching Methods and Properties
The following property and method are relevant only when statement caching is enabled:
OracleCommand.AddToStatementCache property
If statement caching is enabled, having this property set to true (default) adds statements to the cache when they are executed. If statement caching is disabled or if this property is set to false, the executed statement is not cached.
OracleConnection.PurgeStatementCache method
This method purges all the cached statements by closing all open cursors on the database that are associated with the particular connection. Note that statement caching remains enabled after this call.
Connections and Statement Caching
Statement caching is managed separately for each connection. Therefore, executing the same statement on different connections requires parsing once for each connection and caching a separate cursor for each connection.
Pooling and Statement Caching
Pooling and statement caching can be used in conjunction. If connection pooling is enabled and the Statement Cache Purge attribute is set to false, statements executed on each separate connection are cached throughout the lifetime of the pooled connection.If the Statement Cache Purge attribute is set to true, all the cached cursors are freed when the connection is placed back into the pool. When connection pooling is disabled, cursors are cached during the lifetime of the connection, but the cursors are closed when the OracleConnection object is closed or disposed of.
